The Hamlet of Thumble is 3.5, and has a Witch, a Cavalier, and a Shaman
RPGObjects "Legends of Excalibur" will have a slew of new core classes, Arthurian related, it's 3.5
Mercenaries from AEG is 3.0, and has a ton of them (the whole thing is really like an expanded Player's Handbook)
Sovereign Stone is 3.0, and has several good ones. I use the Stalker, the Noble and the Sailor, among others
Deadlands d20 has several (I use the Gunslinger) (It's also 3.0).
Fading Suns d20 has several (I use a lot of them). Most d20 conversions of games have new core classes (and generally can be used in D&D/d20 pretty easily).
Blood & Space has several (I use the Marine and the Doctor). It's 3.0, and science fiction
Torn Asunder is 3.5, and has the Apothecary class, which I use.
Rokugan has the Samurai and the Ninja. You can't have a game without a ninja. It's 3.0
Mongoose has a whole line of "Power Classes", which are dinky $3, 8 page books, each describing a class. I think I have the first 8. They're decent. (The Noble is largely ripped off from Fading Suns d20).
Unhallowed Halls has the Mystic class, IIRC, but it's not very well balanced.
Occult Lore from Atlas has several magical core classes, most of which are pretty good. It's 3.0.
I'm pretty sure Nyambe, also from Atlas, has new African style core classes