May I also suggest BFP2X (also on JKMAG) as well as Al MacDonald's various skinpacks (two of which are posted on that very site).
Also the Rbots mod at rbots.massassi.net is great.
Massassi has some great files in their downloads section, including some unique gametypes like Blaster Tag, JK RPG, MotS CTF, etc. no larger collection of maps exists (Admiral's Command Chambers specializes in Single Player of course).
If you can't find something, just let me know, I have an extensive collection, it may take me awhile to find it, but I can do so.
If you like multiplayer, you owe it to yourself to get MotS. It's too bad you didn't grab the JK+MotS combo pack. You can still probably find it super cheap someplace. If not, there is always Ebay. ; )