Dystopia is probably the BEST free mod i have seen on the source engine so far, it is much more entertaining than the recently released Neotokyo, due to it's wave spawn system instead of a CSS style 1 life per round system.
For those of you who don't know, Dystopia is a cyberpunk themed FPS, with standard shooter elements as well as a unique 'hacking' system.
Here is a link to more info
Here is a link to the download site. It downloads through steam (no external .exe) and it is 100% free, as long as you have ANY source game in your games list (TF2, HL2, CS:S, L4D ect)
Hacking especially takes a bit of practice to pick up, but almost anyone can jump in and enjoy the meatspace combat. I think it would make a great game for respawn, it supports teams of up to 12 v 12, although something around 6 v 6 is a good matchup.
If we could get a dedicated server running then... BONUS! But if not, we should definitely get some games going.