Enemy Mine
I really liked Heroes 4x18. Because of the huge, huge slash potential. Peter/Sylar was always yummy. But this ep really slashed itself. I mean, the whole idea is very old and I've seen it executed way better elsewhere, but it made for a really fun time, especially when I was filling up the blanks myself. ;) I really want to write a J2 AU like that now though. Maybe go back to the basics, and they're soldiers on opposite sides of a war and get stranded in the wilderness somewhere...