There used to be a great many college stations that used an
AM carrier current system. They were extremely low powered but used campus building wiring as their antennas. As long as they conformed to FCC Part 15, they didn't need to be licensed. Since everyone in here loves lists, here is one.
Existing stations
Bulls Radio 1620 - University of South Florida, also heard on licensed WMNF-HD2[1]
KAMP-1570 at the University of Arizona[2]
KANM-1580 at Texas A&M University[3]
KASR-1330 Arizona State University[4]
KDUP-1580 at University of Portland, (Portland, Oregon)
http://kdup.up.edu/
KCIZ 1650 at Mora High School, Mora, Minnesota[5]
KJACK 1680 - Northern Arizona University[6]
KLBC-1610 at Long Beach City College[7]
KMSC-1500 at Minnesota State University Moorhead
KRFH at Humboldt State University
KRIO 1660 at Rio Linda High School
K-ROCKS RadioOne AM Stereo 1670 and AM Stereo 710 in Casper Wyoming [8]
KSSU 1580 AM at California State University, Sacramento
KUR-1670/88.3 at Kutztown University[9]
KUTE-1620 University of Utah[10]
Radio SNHU 1620 at Southern New Hampshire University[11]
WALT-1610 at Davidson College[12]
WERW 1570 AM at Syracuse University
WEXP at La Salle University
WFVS 530 AM and recently LPFM at 100.5 at Fort Valley State University in Fort Valley, Georgia (fiber-optic linked carrier current system)
WGCC 650 AM at Genesee Community College
The WIRE - 1710 AM at the University of Oklahoma
WMAX 540 at Mount Washington College in Manchester, New Hampshire
WNEC 91.7 FM at New England College in Henniker, New Hampshire[13]
Wolfpack Radio-1700 at the University of Nevada[14]
WPPJ-670 Point Park College[15]
WPMD-1700 at Cerritos College[16]
WSIN-1590 at Southern Connecticut State University[17]
WSLU-1620/100.1] at Saint Leo University, St. Leo, Florida[18]
KSUB at Seattle University in conjunction with 8 mW low-power broadcasting and Internet radio[19]
WTBU 640 AM/89.3 FM at Boston University
Radio Laurier Macdonald 560 AM at Laurier Macdonald High School in St. Leonard, Montreal, Quebec, Canada
Former stations
Brown Student Radio at Brown University in Providence, Rhode Island, on A.M. 600.
CHRW-FM at the University of Western Ontario started as a carrier current station at 610 kHz
K.C. AM at Colby College, now WMHB
KARL-AM at Carleton College, now KRLX
KAL at University of California, Berkeley - now KALX
KCC at Chabot College, Hayward, California - now KCRH 89.9
KCWS-AM at Central Washington State College - now KCWU-FM
KDVS, originally KCD at University of California, Davis
KFRH at Washington University in St. Louis - now KWUR-FM
KMPS-AM at University of Alaska Fairbanks - now KSUA-FM
KNAB at Chapman University, Orange, California - ceased carrier current in 1991, now internet-only station ChapmanRadio.com
KOWL at Rice University - now Rice Radio
KRLK 97.5 at Rio Linda High School, California - now KRIO 1660
KSU at Stanford University – now KZSU-FM
KSWC at Southwestern College in Winfield, Kansas - now at 100.3 FM
KUOK at the University of Kansas - now KJHK
WBMB at Baruch College, CUNY; started as a carrier current station at 590AM
WBSC on 640 AM at Bloomsburg State College (now Bloomsburg University) in Bloomsburg, Pennsylvania, but has merged with 91.1 FM WBUQ after that station signed on in 1985. For several years, both stations operated independent of one another prior to the merger.
WCAR 550 AM at the University of North Carolina at Chapel Hill - now WXYC-FM 89.3
WCHP 650 AM at Central Michigan University at Mount Pleasant Michigan
WCUR as WSCS 640 AM, and WCUR 680 AM at West Chester University in West Chester, Pennsylvania, but has since migrated to 91.7 FM, as well as online at wcur.org
WDBS 560 AM at Duke University - now WXDU-FM 88.7
WERU 710 AM/104.7 FM at Embry–Riddle Aeronautical University - now WIKD-LP 102.5
WFAL 1610 AM at Bowling Green State University
WHAT 530 AM at Johns Hopkins University, later WHSR and now WJHU
WHEN 640 AM at the University of Delaware
WHEN at Western Illinois University - now WIUS-FM
WJHU at Johns Hopkins University, Baltimore, Maryland.
WJJX 640AM at the University of Michigan from 1952 to 1987, predecessor to (and previously using the call letters) WCBN now on FM 88.3[20] [21]
WJPZ at Syracuse University, now 89.1 FM
WKC at Knox College, Galesburg, Illinois - now WVKC-FM
WKDU-FM 91.7, the student-run radio station of Drexel University formally WMAX (1958)[22]
WKDT 89.3 FM, the cadet radio station, United States Military Academy, West Point, New York
WLCR-AM 640 (originally WCDW-AM 830) operated by Summer campers at Camp Shaw-Mi-Del-Eca in Lewisburg, West Virginia.
WLKR AM Lake Superior State University, Sault Ste. Marie, Michigan - Now WLSO 90.1 FM "The Sounds of Lake State"
WMTU-FM at Michigan Technological University; started as a carrier-current AM station
WMUC-FM at the University of Maryland, College Park; started in 1937 on 650 AM[23]
WNYU on 800 AM in New York University's dorms at its Lower Manhattan campus
WOCR-650, a "pirate" carrier current station in Ocean City, Maryland, in 1973
WOLF at North Carolina State University in Raleigh, North Carolina - now WKNC
WPSM at Penn State's McKeesport campus (now Penn State Greater Allegheny) - now an internet station WMKP[24]
WQAD/WFQR/WIN/WIUS at Indiana University - now WIUX-LP
WRAF on 590 AM at Binghamton University - now WHRW
WRCR-AM Rockford College[25]
WRCT on 900 AM at Carnegie Mellon University - now WRCT-FM
WRIU Studio B, now only online, at the University of Rhode Island and licensed to Kingston, Rhode Island, on A.M. 580.
WRPS-730 AM at SUNY Potsdam (NY), now WAIH 90.3
WRLC-AM on 1110 and 1150 AM at Rutgers University, now WVPH-FM
WRUR-AM 1090 at the University of Rochester in Rochester, New York - now WRUR-FM; see also campus radio
WSAC 710 AM at St. Anselm College, Goffstown, New Hampshire
WSGR (South Green Radio) at Ohio University in Athens, Ohio
WSOE on 1200 AM at the Milwaukee School of Engineering in Milwaukee, Wisconsin - now WMSE on 91.7 FM
WTGR 530 AM (1969) at Memphis State University in Memphis, Tennessee, now the University of Memphis - now WUMR on 91.7 FM
WUFI-540AM at Florida International University, now WRGP 88.1 & 95.3 FM[26]
WUVT 640 AM at Virginia Tech
WVAT (Voice of Alfred Tech) at SUNY, Alfred, New York - started broadcasting January 1965, now WETD-FM
WVAU on 610 AM at American University, Washington, D.C. (station is still present, but they no longer broadcast carrier current)
WVBU on 640 AM at Bucknell University later licensed to 90.5 MHz FM, carrier current turned off several years later
WVOF on 620 AM at Fairfield University, Connecticut
WVYC 640 AM at York College of Pennsylvania, sister station to FCC-licensed WVYC FM 99.7, also on the Internet
WXOU 88.3 FM at Oakland University in Rochester Hills, Michigan (licensed to Auburn Hills, Michigan)
WXPN and WQHS-730 at the University of Pennsylvania
WYBC/640 at Yale University[27]
Those lists are from Wikipedia. I noticed that WNFT from Slippery Rock is not included. I don't know how many other college carrier current stations are omitted.