Well, if you've already played PSG's mods I'm not sure I have anything else to recommend. I guess if you're really scouring for one, try looking through the quickie guide for some older gems (I think Runelancer's were pretty good).
Well, I'll list the ones which I played recently, and say if they were worth it, I guess...
- Schism (heck yes)
- [not a] MOD (that was great, really)
- CS2 (some new mod around here, broken doors and behemoth & deathtrap challenge with no reward, not recommended)
- RAVE (great mod)
- GOST KITTENZ (no)
- Speed Story (meh, it's just Cave Story on drugs/coffee)
- CSTSF Mod (interesting one)
- Cave Story Redesign (despite so many nice features, it's not really fun to play...)
- Obscuro Lumen Venemum Aeris (meh, but still better than GOST or Before Story)
- Ama (very interesting, yet I feel something's missing in it)
I don't remember playing anything more recently...