David Eddings
The system of magic, widely praised in Eragon, is ripped straight from David Eddings' universe. Not only can magic casters not exceed spells that would require more strength than is in their body, but magicians must be super careful to phrase or think everything precisely as they intend it, or face dire consequences. If that's not enough, the silvery mark on Eragon's hand is ripped straight from the Belgariad, where Garion has exactly the same mark.
In addition, the chapter of the bridge crossing - tricking the tollman - comes straight from David Eddings' 'the Ruby Knight', almost word for word.
Oh, and that fiery blue sword? Guess where that came from...
Tolkien
If you haven't seen these links, then I feel sorry for you. Most fantasy writers make an attempt at originality, but no, that's not for Christopher Paolini. His description of Arya matches, almost word for word, the description of Arwen, who bears a remarkably similar name. Oh, and Eragon/Aragorn. Huh.
What else, what else? Other than most of the names, which have only a couple of letters changed,[footnote]There's a proper list here http://telpenori.blogspot.com/2007/02/paolini-and-plagiarism_28.html[/footnote] there are also the characteristics of elves and dwarves, and so on.
Star Wars
Brom is essentially a mix of Gandalf and Obi-Wan Kenobi, while the entire plot is ripped straight from these films. Refer to the link at the bottom, if you don't believe me. What else? riders/glowy magic swords and jedi/lightsabers. Woa, that's crazy. Not to mention that the ancient force of lawkeepers was wiped out by one of their own, who then took an apprentice and is trying to kill the inheritor of the jedi/dragon rider legacy. Fuck, I'm going into too much detail. Just read the link.
Wheel of Time
Okay, small boy starts on a farm, father gravely wounded by poisoned blade, leaves with ancient guardian to fight old evil. It's a toss-up as to whether that's from Star Wars or WoT, but there's some other stuff as well.
For instance, Roran. His character is simply a badly written carbon copy of Perrin. They both lose their wives to the evil forces, neglect the people under their leadership, become utterly desperate to rescue her, have leadership and self confidence, and, on top of all that, they both go around killing people with FUCKING HAMMERS. Or that could all just be a coincidence. You tell me.
Ursula Le Guin
There are a couple of links here, but the main one is the ancient language. the Wizard of Earthsea was this magical land, where in the ancient tongue, everything had a name by which it could be controlled, and that was how magicians exercised their power. Sound familiar?
Magician
There are a couple of things that could come from either this or The Dragonriders of Pern, but, essentially, Eragon has a lot in common with Tomas of Midkemia. Tomas befriends a dragon, and becomes the inheritor of the legacy of the Valheru, an ancient race of Dragon lords/riders that once roamed the world. Also, once he takes on that mantle, his features become more sculpted, more alien, and he goes off and woos the elven queen. Again, can you see any links to Eragon here?
The Dragonriders of Pern
Essentially, most of this is in the title, but one of the important things here is the telepathic link between riders and their dragons.
Terry Pratchett
I'm getting a little sick of writing now, but read through the first five Discworld novels, and take a shot of whisky every time you read something that popped up in Eragon. I assure you, you'll be roaring drunk by the end.
There's more, far more, but I can't be bothered to get into it, any more. Just rest assured that Eragon is in no way, shape or form original, and that it should never have been published.