I got Song and Silence, Defenders of the Faith, Forgotten Realms, Sword and Fist, and Tome and Blood. I keep hearing a lot about this dragon book but I don't know what it is. Can somebody help me out?
From the looks of it, you've only gotten WotC D&D products so far. It might be worth checking out some D20 products.
My D20 System Guide should help - has details (and reviews of) most D20 products out there (including all the WotC ones). Be warned, though, there are hundreds of them!
Dragon is also a monthly D&D magazine, and is fairly popular and gets mentioned rather often in conversations, which might also be what you mean... Here's the website: http://www.wizards.com/default.asp?x=dragon
If you're going to stick to WoTC material (which I think is a good idea when you don't own a lot of stuff yet), my recommendations would be:
Forgotten Realms stuff: Magic of Faerun (still the best magic book IMO), Lords of Darkness (really helps the newbie DM - like me)
General D&D: Masters of the Wild (you'll want to complete your splatbook collection), Manual of the Planes (for the more advanced DM and not completely compatible with FR, but what a great book! will give you a great idea of just how far you can go with 3rd edition D&D)
BTW, Song & Silence is the worst WoTC book I've read so far, so you can't go downhill from there (though apparantly the Hero Builder's Guidebook and Enemies and Allies are pretty lame too). In contrast, DoTF and S&F are both rather unimaginative but solid, useful books. T&B I really liked. The FRCS finally is still the ultimate D&D book, haven't seen anything even remotly as good yet (including core books). Even people who hate the FR drool over that book and wish someone would make a similar one for their campaign setting. Just warning you so you don't expect another FRCS when you buy your next book - there simply isn't any other book of that quality out there.
Also there's plenty of stuff for you, both as player and as DM to choose from in the d20 world. I know for me, it depends on what I can add into an existing campaign. But regardless, I'm sort of the defacto guy for anything related to the Scarred Lands and the occcasional S&SS product.
Actually, beyond the core books, I'd start looking at the reviews. Quite a bit of good stuff is out there, sometimes at a better price than WotC. And don't hesitate to buy a PDF! Just because two middlemen aren't taking a cut doesn't mean it's not any good.