I'm not sure if the poster is asking about 3rd party stuff that was contemporary with the old TSR products, or is asking about 3rd party stuff that's being put out right now.
If he's asking about older stuff, Judges Guild actually had a license from about 1976 to 1980. Mayfair Games "Role Aids" line was not licensed, but was billed as compatable with AD&D. They put out stuff from the early 80's to early 90's.
Then there was a whole bunch of "generic" products that were for D&D in everything but name. Some of these started as D&D supplements and then grew into their own game... ICE's Arms Law, Spell Law, etc. became Role Master, Emperor's Choice's Arduin went from supplemets to their own game, etc.
But many more were just D&D supplements with the serial numbers filed off... Chaosium's All the World's Monsters volumes, Midkemia's cities, Flying Buffalo's Grimtooth's Traps series, Columbia's early Harn stuff before they put out Harnmaster, etc., etc.
I'm barely scratching the surface here.
The afterglow website did a great job cataloguing it all. Unfortunately, it is no longer up. This
site has tried to replace it. It doesn't have as much content, but has more pictures.
If the poster is asking about new stuff for the old editions, the lulu link posted up thread is a good place to start. Also see:
Pied Piper Publishers (Rob Kuntz's company)
Goodman Games, both for their generic products (esp. Points of Light) and the odd 1e special
FES's Monsters of Myth, which is available through Lulu, but oddly not linked to on the Lulu OSR page
And of course, Dragonsfoot is a fan site that puts out a lot of professional quality stuff for free.