VICE keys are used to encrypt the game's weapon config files in an effort to make them more difficult to tamper with. It's not really a great protection, as usually the key is just hardcoded into the server binaries. Some games, such as Golden Eye Source, try to make it more difficult to retrieve these, but even then it's trivial.
These keys can be used to decrypt the CTX files that many games provide.
|Counter-Strike: Source / Global Offensive||d7NSuLq2|
|Day of Defeat: Source||Wl0u5B3F|
|Dystopia 1.3 RC2||G8stUh3F|
|Golden Eye Source||Gr3naDes|
|Half-Life 2: Capture the Flag 2.1||R1dj3axP|
|Half-Life 2: Deathmatch||x9Ke0BY7|
|Left 4 Dead 2 (VScript .nuc)||SDhfi878|
|No More Room In Hell||lREeeapA|
|TF2 (everything else)||E2NcUkG2|