Get Battlefield 2. You'd have to download a few maps, maybe a single player mod, and edit the ai file to have large scale battles, but it's worth it.
CnC games
Also known as: watching bots send sizeable armies at eachother once, and then keep sending only one soldier ever after.
It gets pretty intense like that y'no.
yeah bf2 is really good even with just bots
Pretty sure Timesplitters 2 could have bots only.
TF2's Easy bots are pretty fun to watch too.