I watched Avatar a few times now and one thing that is very noticeable to any James Cameron fan is the number of similarities between Avatar and Aliens.

In no particular order :

Cryogenic-sleep
Drop-ships
Power-loader-exo-skeletons
References to "The Company"
Motion trackers
Nasty Company representative who happily puts profits over lives
Strong Latino woman who sacrifices herself for the greater good
Power-loader-exo-skeleton fights alien
Sigourney Weaver
Organic vs Machine

... but Aliens and Avatar are both brilliant so I'll forgive Jim Cameron just this once.