I just dug my OG Xbox out of storage yesterday. If you can track one down, definitely get a mod chip put in and get your self bigger hard drive. I had a Xenium chip that didn't require any soldering, just plug it in, however I eventually replaced it with an Xecuter 3 since you can do a lot more with that one.
As far as games go: Halo 1 & 2, Mechassault, Forza, Jade Empire, Star Wars Knight of the Old Republic, Dead or Alive 3, Need For Speed Underground, Elder Scrolls Morrowind, Sega GT.