Under FCC regulations, FM broadcast stations in "Zone I" (most of the northeastern U.S., as far west as Barneveld, Wisconsin, and south roughly to the Ohio River and southern borders of Virginia and West Virginia) and "Zone IA" (California south of Red Bluff) are limited to a maximum power of 50,000 watts at a maximum antenna height of 150 meters. (500') Stations in "Zone II" (everywhere else..) are allowed 100,000 watts at a maximum of 600 meters. (2000') Stations may use higher antennas if they reduce power to compensate.
But these regulations haven't existed forever. Some (actually, quite a few) stations were built before they went into effect, and those whose powers were already above the new limits were allowed to keep their excess power. The table below shows these "superpower FMs". I do not guarantee 100% accuracy here, but I think it's pretty much correct...
The "s/b" column shows the maximum power that would be granted today at the antenna height the station is using. HAAT is the station's antenna height above average terrain, in meters. Multiply by 3 to get feet. (more or less..) "Class" indicates which zone the station is in; Class B stations are assigned in zones I and IA; Class C in Zone II. "dB" is how many decibels "overpower" the station is - how much its actual power exceeds what it should have under current regulations.
State City Call Freq ERP s/b HAAT Class dB Signon CA Santa Barbara KRUZ 103.3 105,000 1,380 903 B 18.8 8 Aug 1961 CA Los Angeles KPFK 90.7 110,000 1,511 863 B 18.6 26 Jul 1959 CA Los Angeles KBIG 104.3 84,000 1,446 882 B 17.6 15 Feb 1959 CA Los Angeles KLOS 95.5 61,000 1,236 954 B 16.9 30 Dec 1947 CA Los Angeles KRTH 101.1 51,000 1,236 954 B 16.2 1941 CA Los Angeles KTWV 94.7 52,000 1,511 863 B 15.4 7 Mar 1961 CA Los Angeles KKBT 92.3 42,000 1,430 887 B 14.7 29 Dec 1948 CA Los Angeles KCBS-FM 93.1 28,500 990 1,066 B 14.6 1948 CA Los Angeles KUSC 91.5 39,000 1,417 891 B 14.4 1946 CA Los Angeles KLVE 107.5 29,500 1,347 914 B 13.4 2 May 1959 CA Fresno KSKS 93.7 68,000 3,344 580 B 13.1 1946 CA Riverside KSSE 97.5 72,000 3,626 557 B 13.0 17 Mar 1959 CA Los Angeles KPWR 105.9 25,000 1,315 925 B 12.8 20 Dec 1956 NY Buffalo WMJQ 102.5 110,000 6,758 408 B 12.1 11 Nov 1946 MI Grand Rapids WBCT 93.7 320,000 19,861 238 B 12.1 Oct 1951 CA Los Angeles KLSX 97.1 21,000 1,344 915 B 11.9 1954 CA Los Angeles KZLA-FM 93.9 18,500 1,231 956 B 11.8 7 Aug 1957 CA San Francisco KQED-FM 88.5 110,000 7,512 387 B 11.7 Jun 1969* MI Grand Rapids WOOD-FM 105.7 265,000 18,440 247 B 11.6 1962 CA San Francisco KIOI 101.3 125,000 8,977 354 B 11.4 27 Oct 1957 CA Los Angeles KKGO-FM 105.1 18,000 1,453 880 B 10.9 18 Feb 1959 CA Santa Barbara KHTY 97.5 16,000 1,420 890 B 10.5 1 Sep 1957 CA Los Angeles KOST 103.5 12,500 1,249 949 B 10.0 9 Oct 1957 CA San Francisco KMEL 106.1 69,000 7,284 393 B 9.8 30 Nov 1960 CA Monterey KWAV 96.9 18,000 2,016 747 B 9.5 14 Oct 1961 CA Los Angeles KYSR 98.7 75,000 8,681 360 B 9.4 30 Jun 1954 CA Berkeley KPFA 94.1 59,000 6,859 405 B 9.3 Apr 1949 CA San Francisco KEAR 106.9 80,000 9,675 341 B 9.2 1958 CA San Jose KBRG 100.3 14,500 1,821 786 B 9.0 4 Mar 1963 CA Salinas KDON 102.5 18,500 2,349 692 B 9.0 Dec 1959 CA San Francisco KISQ 98.1 100,000 13,104 293 B 8.8 17 Jul 1958 CA Los Angeles KKLA-FM 99.5 10,500 1,459 878 B 8.6 1985* PA Williamsport WKSB 102.7 53,000 7,512 387 B 8.5 1 Apr 1948 CA San Francisco KLLC 97.3 82,000 11,782 309 B 8.4 1 Mar 1963 PR San Juan WIPR-FM 91.3 105,000 15,545 825 B 8.3 3 Jun 1960 CA San Bernardino KOLA 99.9 29,500 4,377 507 B 8.3 15 Jun 1959 IL Urbana WILL-FM 90.9 105,000 16,771 259 B 8.0 1 Sep 1941 CA Los Angeles KIIS-FM 102.7 8,000 1,383 902 B 7.6 1948 MI East Lansing WKAR-FM 90.5 86,000 15,095 273 B 7.6 10 Oct 1948 CA San Francisco KFRC-FM 99.7 40,000 7,174 396 B 7.5 1949 PA Johnstown WKYE 95.5 57,000 10,783 323 B 7.2 Aug 1949 WI Baraboo WOLX 94.9 37,000 7,174 396 B 7.1 3 Mar 1946 CA San Francisco KOIT-FM 96.5 24,000 4,883 480 B 6.9 1959 CA Ventura KHAY 100.7 39,000 8,262 369 B 6.7 1 Jan 1962 OH Dayton WHKO 99.1 50,000 10,651 325 B 6.7 1946 MI Ann Arbor WUOM 91.7 93,000 19,861 238 B 6.7 1948 CA Santa Barbara KTYD 99.9 34,000 7,396 390 B 6.6 11 Aug 1962 CA San Luis Obispo KZOZ 93.3 23,000 5,050 472 B 6.6 (unknown) MI Bay City WIOG 102.5 86,000 18,896 244 B 6.6 12 Nov 1961 OH Columbus WNCI 97.9 175,000 38,473 171 B 6.6 Jul 1961 NY Buffalo WNED-FM 94.5 105,000 24,113 216 B 6.4 6 Jun 1960 VA Richmond WRVQ 94.5 200,000 50,000 107 B 6.0 4 Aug 1948 CA Los Angeles KIBB 100.3 5,300 1,341 916 B 6.0 1 Jun 1957 MI Detroit WOMC 104.3 190,000 50,000 110 B 5.8 5 Mar 1948 NY Buffalo WDCX 99.5 110,000 29,586 195 B 5.7 Feb 1963 VA Winchester WINC-FM 92.5 22,000 5,973 434 B 5.7 Oct 1946 CA San Francisco KYLD 94.9 30,000 8,262 369 B 5.6 12 Mar 1958 IN Bloomington WTTS 92.3 37,000 10,206 332 B 5.6 7 Jan 1960 NY Syracuse WYYY 94.5 100,000 28,696 198 B 5.4 1946 NY Syracuse WNTQ 93.1 97,000 27,846 201 B 5.4 1956 MA Boston WGBH 89.7 98,000 28,696 198 B 5.3 6 Oct 1951 MI Grand Rapids WVGR 104.1 108,000 33,593 183 B 5.1 7 Dec 1961 NY Albany WAMC 90.3 10,000 3,125 600 B 5.1 1 Oct 1958 WI Delafield WHAD 90.7 79,000 24,797 213 B 5.0 30 May 1948 CA Glendale KSCA 101.9 4,800 1,511 863 B 5.0 Mar 1951 CA San Diego KJQY 94.1 100,000 31,830 188 B 5.0 1949 WV Beckley WJLS-FM 99.5 34,000 10,986 320 B 4.9 6 Nov 1946 IN Indianapolis WFBQ 94.7 58,000 18,742 245 B 4.9 26 Nov 1959 PA Pittsburgh WLTJ 92.9 47,000 15,318 271 B 4.9 4 Apr 1942 PA Pittsburgh WDVE 102.5 55,000 18,000 250 B 4.9 10 May 1962 CA San Francisco KDFC-FM 102.1 33,000 11,055 319 B 4.7 1 Dec 1947 VA Richmond WTVR-FM 98.1 50,000 17,166 256 B 4.6 Feb 1946 TN Memphis WMC-FM 99.7 290,000 100,000 277 C 4.6 22 May 1947 PA Pittsburgh WWSW-FM 94.5 50,000 18,440 247 B 4.3 1940 WI Madison WERN 88.7 20,500 7,590 385 B 4.3 30 Mar 1947 VA Norfolk WVKL 95.7 40,000 15,663 268 B 4.1 21 Sep 1961 NY Buffalo WLCE 92.9 91,000 35,909 177 B 4.0 1947 DC Washington WETA 90.9 75,000 32,518 186 B 3.6 19 Apr 1970* CA Sacramento KZZO 100.5 115,000 50,000 100 B 3.6 Oct 1958 CA Mountain Pass KHYZ 99.5 8,400 3,706 551 B 3.6 Apr 1980* PA Altoona WFGY 98.1 30,000 13,658 287 B 3.4 17 Oct 1960 NY Utica WFRG 104.3 100,000 50,000 151 B 3.0 10 Oct 1948 MI Detroit WKQI 95.5 100,000 50,000 131 B 3.0 12 Feb 1949 IL Chicago WMBI-FM 90.1 100,000 50,000 134 B 3.0 25 Jul 1960 CA San Francisco KITS 105.3 15,000 8,398 366 B 2.5 1 Jun 1964 OH Salem WQXK 105.1 88,000 50,000 131 B 2.5 25 Nov 1958 IL Chicago WFMT 98.7 15,500 8,827 357 B 2.4 13 Dec 1951 NH Mt. Washington WHOM 94.9 48,000 27,652 1,141 C 2.4 9 Jul 1958 CA Stockton KSTN-FM 107.3 8,100 4,666 491 B 2.4 1962 MI Detroit WRIF 101.1 27,000 15,663 268 B 2.4 1 Jan 1948 OH Cleveland WMJI 105.7 16,000 9,507 344 B 2.3 4 Nov 1954 NY Ithaca WYXL 97.3 26,000 15,663 268 B 2.2 1 Sep 1947 MI Detroit WDET-FM 101.9 79,000 50,000 137 B 2.0 18 Dec 1948 VA Roanoke WSLQ 99.1 150,000 100,000 607 C 1.8 1 Nov 1947 VA Newport News WGH-FM 97.3 74,000 50,000 120 B 1.7 Nov 1948 MI Detroit WWWW 106.7 61,000 42,343 163 B 1.6 16 Oct 1960 PA Pittsburgh WXDX 105.9 72,000 50,000 131 B 1.6 1960 CA San Francisco KKSF 103.7 7,800 5,605 448 B 1.4 3 Nov 1947 WV Huntington WKEE 100.5 53,000 38,473 171 B 1.4 19 Nov 1947 CA San Francisco KFOG 104.5 7,100 5,340 459 B 1.2 1 Mar 1963 IL Mount Vernon WMIX-FM 94.1 50,000 39,860 168 B 1.0 1946 OH Toledo WIOT 104.7 50,000 41,322 165 B 0.8 Oct 1949 WA Edmonds KCMS 105.3 115,000 100,000 220 C1 0.6 11 Mar 1960 IA Des Moines KHKI 97.3 115,000 100,000 137 C1 0.6 1961 PA Montrose WPEL-FM 96.5 57,000 50,000 140 B 0.6 5 Jun 1961 NE Omaha KGOR 99.9 110,000 100,000 375 C 0.4 1959 CA Los Angeles KFSG 96.3 54,000 50,000 146 B 0.3 1949 IL Decatur WSOY-FM 102.9 54,000 50,000 137 B 0.3 Nov 1946 OH Wooster WQKT 104.5 52,000 50,000 101 B 0.2 1947* The current limits went into effect in 1962. Stations marked with a * signed on after that date. Most signing on a year or two later probably already held construction permits but had not yet completed construction. I cannot explain how WETA received a superpower permit 8 years after the limits were set. KQED took over the facilities of a religious station that dated back to at least 1966 and almost certainly earlier. The 1985 signon of KKLA-FM is the date under the current license. Another license for the same technical facilities had existed earlier, but was revoked in the mid-1980s for violations of FCC regulations. KHYZ received special dispensation from the FCC due to the lack of other FM service in that isolated area.