I love Battle Royale. It's such a trip... it didn't seem incredibly inventive but a great ride.
Did you know that Chiyaki Kuriyama from Battle Royale was in Kill Bill, as O-Ren's psycho bodyguard? She stole that film IMHO.
It may be hard to find a rental but the VCD should be pretty easy to obtain. Poker Industries has it for $9
here.