It's a very good idea to have both a raster program (like Photoshop) and a vector program (like Illustrator). The most popular alternative is Corel. Current version is called Corel Graphics Suite X3. It includes Corel Draw (vector), Corel Photopaint (raster) and the very handy Corel PowerTrace. It's much cheaper than the Adobe products. See the thread
What did you pay for Corel X3 for price range.
A free trial download is available from Corel.com.
I think Corel offers the best bang for your buck. Others disagree.
There are all kinds of tutorials and extras available for Corel, like the excellent
T-shirt Comp Plugin.