I've been a cubicle rat going on 20 years now. Posters, my kids' artwork, wall calendars with bands or trains, anything to make it "personal". Stuff I would've put on my dorm room walls 30 years ago, but which don't have any place on the walls in a family home.
As for on the desk, you've already gotten some great suggestions. A real plant and a real lamp. Once again, something to personal it as your space. Something beyond the company-issue generic office supplies. I keep a small abacus sitting next to my calculator. Both were gifts, and it was a while before I realized the symbolic symmetry of having both of them.