Remember The Xbox. The Console That Started It All.

[DirtyP2002]

Halo 1, Halo 2
Fable
Shen Mue I + II
Yager
Splinter Cell
Doom 3
Tom Clancys Ghost Recon (online was great)
Ninja Gaiden
TopSpin (online was freaking awesome)

And a lot of games that were just awesome with online play, but XBL is down on the original Xbox, so it doesn't make any sense.