Burning Man (type it in on Google Earth - amazing)
Guano Valley (fun little tour)
Hart Mtn (Hot Springs, artifacts, kayak, tour
Sheldon National Antelope Refuge (vast empty area)
Pueblo Mtns (old mines, exloring, archeology)
Steens (snowed in until July)
Alvord Desert (fun exploring, hot springs, mines)
Trout Creek Mtns (fun exploring, hot springs, ??)
Hot Springs Range (need to get there some day)
Owyhee's (incredible exploring but mostly private)
I'm sure I'm missing a few good areas
If it's a long weekend only one location would really work, then day trip in/out, have fun, go home.
I have not spent enough time in any of these places (including the 24 years of work/play in the Steens/Alvord area) to get tired of exploring. 90% of it does not require 4x4, just high clearance and good judgment. I'd like to explore Sheldon NWP in more detail, I've heard great things about it and have never spent anytime off pavement exploring.
Bob