The Longest Yard/The Mean Machine from the 1970s with Burt Reynolds (It's been remade as The Longest Yard in the US with Adam Sandler and Burt in a cameo role and as TMM in the UK with Vinnie Jones).
Lockup with Sylvester Stallone
If you fancy a longer investment, try season one of Prison Break, the tv show from the mid/late 00s.
If you want something more thoughtful than Con Air and the like, the ultimate prison movie is the Shawshank Redemption. The Birdman of Alcatraz is also a must-see. Ditto Escape from Alcatraz (Clint Eastwood), Cool Hand Luke (Paul Newman) and the under-rated comedy life with Eddie Murphy.