If you have $150 then the HD5770 is the obvious choice or maybe waiting a tad for the GTS 450 to be on the market.
The GTS 250 and HD4850 should only be considered if you would really like to keep the price closer to $100 or have a low resolution monitor(1280x1024 and below) or a CPU which wouldn't benefit from a better card.
At that resolution and if you care about DX11 then the HD5770 is the default choice. But as advised waiting for the GTS450 and the HD6xxx cards would be wise. Lets hope HD6xxx has some cards in your price range.