Girls in Prison (1956) 21 year old Anne Carson gets convicted of bank robbery, protesting her innocence all the time. Once inside she meets a whole gang of WIP archetypes. Being a 1950s cautionary tale, there's a lot more innuendo than in-yer-end-hole, but this is a true pioneer of the genre.
Girl on a Chain Gang (1965) This exploiter is based on the same murder of civil rights workers that "Mississippi Burning" was, except it's just a GREAT DEAL more sleazy. In this one the three freedom-riders are nice looking girls.
Sweet Sugar (1972) Phyllis Davis stars as a pretty young thing unjustly sent to a brutal Central Ammerican women's prison, where she is unjustly tortured and humiliated.
Ilsa, Harem Keeper of the Oil Sheiks (1976) Okay, this isn't really a WIP flick, but it has almost all of the same elements, with the addition of some cheap Persian rugs and some head towels. Ilsa, unemployed since the closing of the concentration camps, gets work minding the harem of an a-rab sheik. Rape, torure, humiliation, just like a prison.
Women in Fury (1984) Tough-ass group of severely abused women inmates plan and execute an escape from their brutal jailers, only to find themselves in the equally brutal Amazon jungle.
Prison Heat (1986) Horrific Asian prison houses beautiful babes at the mercy of sadistic gaurds. Lots of leering Asian men ogling naked and helpless captives.
Reform School Girls (1986) Take-off on the WIP genre, with Sybil Danning and Plasmatics singer (and former porno porno actress) Wendy O. Williams.
10 Violent Wome (1989) Ten good-looking babes are caught trying to puul off a jemelry heist, and are then sent a brutal women's prison, where they get creative in finding ways to get out. Direct by Ted V. Mikels.
Caged Fear (1992) David Keith plays a no-account who gets his girlfriend sent to prison. Then he manages to sneak inside (disguised as the new warden!)in hopes of helping her escape. We have a savage lesbian gang, and also a sympathetic lesbian victim of said gang. We have a crazy prisoner riot with screaming loonies. We have a mean-spirited lesbian prison director and a lecherous male guard. Not nearly enough nudity and totally senseless violence to make this a great exploitation flick.
Chained Heat II (1993) is by far ONE OF the weirdest of these, with huge Brigitte Neilson as the sadistic (of Course) dominatrix that runs a Chzech women's prison (I'm not sure if this before or after the fall of the wall), and she sure can chew up the scenary. I felt sorry for Sylvester Stallone just watching her strut around in her bondage gear (I bet he got a ass whippin every night!). This one is the strongest on the lesbian angle, with all the other assorted sadists and victims as well. It comes close to being Great.
Caged Heat II (1994) is probably The Best of the lot. It's made in the Phillipines and nobody can make exploitation flicks like them filipinos. I mean this is dirt-tee. Jewel Sheppard gets strip-searched by the warden with the help of one of his guards. And of course we get a little lesbian action as well. The story is...well, who cares about the story. This is not cinema. This is a true drive-in movie, with lots of evil Asians and nekkid gals. Great is the only way to discribe it. Sleazy would also be appropriate.