If you're looking for an OpenGL pixel shader, the latest version is 4.1.
This card:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814125359Being one of the cheapest you can find supports up to OpenGL3.1 and DirectX 10.1.
If you're looking to purchase a video card, make sure your motherboard has the appropriate slots for it.
That card I linked is a PCI Express 2.0.
The other types could be AGP or just plain PCI.
http://www.save25percent.org/wp-content/plugins/rss-poster/cache/b80b0_card-diagrams.jpg
Look inside your computer.