Midsommer Murders (1998) as Peter Drinkwater
Wilde (1998) as Rentboy
The Lord Of The Rings:The fellowship of the ring (2001) as Legolas
Black Hawk Down (2002) as Private First Class Todd Blackburn
Ali G in da house (2002) as Lance
Deed Poll (2002) as Sean Poll
Lullaby of Clubland (2002) as Finney
The Lord Of The Rings:The two Towers (2002) as Legolas
The Lord Of The Rings:The return of the king (2003) as Legolas

Orlando's performance in The Lord Of The Rings:The Fellowship Of The ring seems to go beyond performance: he sinks so deeply into the role of Legolas, that you almost forget he's Orlando. This film was his major film debut.
(I'm surprised he hasn't been in anything else!)