1) Large work surface with no obstructions: No hutch, no little integrated file areas, etc.
2) Unobstructed leg room. Nothing is worse than those old wooden desks where your legs are confined to a tiny little area. I like to sprawl out.
3) Sturdy construction, doesn't wobble, etc.
That's it for me. I basically just want a nice table. If I need a file cabinet, I'll add one. If I have other storage needs, I'll add them. I hate desks that try to integrate everything all into one, and I especially hate desks that have keyboard trays.