Eragon is shit. Seriously, you should return it. I don’t care if the author is 17. If you write a book that so brazenly rips off other books (namely Lord of the Rings and the Wizard of Earthsea, set to the plot of Star Wars), you don’t deserve money. In fact, you should be thrown in jail.
I second (third/fourth) His Dark Materials and The Neverending Story. Both are some of the most creative fantasy out there. You also might want to check out the Bartimaeus Trilogy. It’s vaguely reminiscent of Harry Potter in that it’s about a kid wizard in England, but it’s significantly more jaded and political, and the nature of the magic is pretty interesting (“magic” basically involves enslaving demons and telling them to do stuff for you). You’ll like it if you liked the later HP books.
Finally, if you want some really adult fantasy, George R. R. Martin’s A Song of Ice and Fire series is good. It’s unfinished (4 out of 7), extremely long, and extremely violent and merciless to its characters. I only read the first one but other nerds swear by it.
Oh! Almost forgot. The Chronicles of Amber, by Roger Zelazny. (Well, the first five. I’m told the last five suck.) Really awesome, “adult” but not excessively dark like Martin’s, and extremely creative. Neil Gaiman recommends. Actually I’m surprised nobody (ahem, EP) recommended any Gaiman books.
Also: I mentioned Eragon rips off the Wizard of Earthsea, by Ursula LeGuin, which you might like. There’s four books. The first is pretty good, the second is great, the third is bla, and I didn’t read the fourth one.