I am here to announce some of the best, yet very unknown, mods:
1. Redemption: single-player, comes with cs retail. You can probably get it on KaZaA or something if you don't have cs retail.
2. Wanted: multiplayer, again, comes with cs retail.
3. Goldeneye: multiplayer, find it at planethalflife.com. I think its there. Its N64's goldeneye with the same weapons and levels, only it is online.
4. Deathmatch Classic: multiplayer, Should come with Half Life update patches. Great game, but played very little.