Here is the full list of all 37 Eragon achievements worth 1,000 gamerscore. It takes around 8-10 hours to unlock all of the achievements on Xbox 360.
You have beaten the RA'ZAC CHASE level on HARD.
You have made it through the DARET BRIDGE level on HARD.
You have made it through the DARET TOWN level on HARD.
You have made it through the DARET DOCKS level on HARD.
You have made it through the SPINE MOUNTAINS level on HARD.
You have made it through the CARVAHALL level on HARD.
You have made it through the CARVAHALL level on NORMAL.
You have made it through the SPINE MOUNTAINS level on NORMAL.
You have collected all the secret eggs