Quake 3 Files
GTKRadiant 1.1 TA (9.68MB)
In my opinion the BEST map editor for Quake 3. A MUST if you want to get into Quake 3 mapping.

IK2K Base - Texture Set (23.8MB)
A HUGE set of textures from the IK2K Base level range (Note: I did NOT make this).

Half Life Files
Worldcraft Version 3.3 (1.91MB)
In my opinion the BEST map editor for Half-Life. A MUST if you want to get into Half-Life mapping.

(Note - I take no responsibility for any damage these files cause to your system (I have virus scanned them, and I have a virus guard, but you never know so I am writing this to be safe))