This is the first article in series of (planed) three. I intend to write down every character that was ever mentioned by name and maybe add a physical discritipion and some background, so if you haven't read the book and if you don't want to find out yet, don't read this, since it probably includes some SPOILERS!
The main point of this is to find all characters that appear in all three books, so that we may guess who the third Raider is!
So lets do this! *incredibly optimistic face*

Characters that actualy appear:
Arya - an elf, black hair, dark green eyes
Eragon - 15 years, brown eyes
Sloan - butcher, black eyes, pale
Katrina - 16 years, tall
Horst - blacksmith
Albriech - Horst's son
Baldor - Horst's son
Roran - Eragon's cousin, 17 years,
Merlock - trader
Morn - owner of inn
Saphira - Eragon's dragon
Dempton - stranger from Therinsford
Gertrude - healer
Elain - Horst's wife, small, slim, blonde hair
Haberth - man from Therinsford who sold horses to Brom and Eragon
Trevor - man from Daret
Gareth - innkeeper from Teirm
Martin - man from Gareth's inn
Jeod - Brom's friend, ally to the Varden
Angela - herbalist who lives at Teirm
Helen - Jeod's wife
Solembum - werecat
Brand - administrator in Teirm
Marcus Tabor - ruler of Dras-Leona
Murtagh - 18 years, dark brow hair
Dormnad - Brom's friend from Gil'ead
Orik - dwarf that saves Eragon from water
Twins - two identical bald men magicians that work for Varden
Ajihad - king of Varden
Hrothgar - king of dwarfs
Nasuada - Ajihad's daughter, about 17 years
Fredrik - dwarf
Jörmundur - Ajihad's right hand
Togira Ikonoka - The-Criple-Who-Is-Whole

Characters that appear, but die until the end of the book (bold) and characters that are already dead by the begging of the book (italics)
Durza - a Shade with red hair, and maroon eyes; killed by Eragon
Garrow- Eragon's uncle, Roran's father; killed by Ra'Zacs
Marian - Garrow's dead wife, Roran's mother
Ismira - Sloan's dead wife
Selena - Eragon's dead mother
Brom - an old storyteller, has white beard, latter he reavels to be a Rider; killed by Ra'Zacs
Morzan - Rider, Forsworn; killed more than 15 years ago by Brom
Vrael - leader of Riders, killed by Galbatorix
Saphira - Brom's dragon, killed by Forsworn
Torkenbrand - slave trader that Murtagh kills
Deynor - Ajihad's precursor
Laetri - an elf that survived killing a Shade
Imstad - a Rider that survived killing a shade
Korgan - Hrothgar's ancestor
Dondar - 12th king of dwarfs
Tornac - Murtagh's servant that helped him escape from Galbatorix, but died while doing it

Characters that are only mentioned:
Galbatorix - king, Rider, has black eyes
Islanzadi - queen of elves
Orrin - king of Surda
Shruikan -Galbatox's second (and current) dragon

Note: It is quite possible that I have missed a few characters so fell free to tell if you find some.