Do you have any particular requirements or budget for your upgrade?
As Your Computer does have a free 16x PCIe slot, you could conceivably use any current GPU.
Unfortunately, your PSU is only rated to 250W which will extremely limit your choices with out further upgrades.
Your safest option would be either an AMD 5450 (19.1W) or AMD 6450 (27W).
You could also try a more powerful AMD 5570, but its higher 42.7W ceiling may be an issue.
The next most powerful GPUs all take 60W or more, which I would not recommend with your current PSU.