We had this on an old server, I found that it increased player's stake in the game and each round's outcome for their team.
Very simple: before each round, players can bet up to a certain amount on if they think they can win next round. The one I'm used to was a simple !bet menu.
The usual...
Very simple: C4 Mania.
Essentially bomb rush but with C4, everyone gets some and you just try and survive as everything goes nuclear 45-50 seconds into the round.