I've recently purchased a tournament edition round 2 fightstick for SFIV, and i'd have to say it was probably one of my better gaming investments.
It takes getting used to at first, but once you get used to the controls, it's well worth it. The buttons are solid and the stick works great, and it is easy to place on your lap or on a surface while playing.
It's USB so it can also plug into the computer and work with programs such as GGPO or 2dfighter.
There are many different versions made by Madkatz; all of which have excellent offers over Newegg.com.
SFIV standard edition fightstick-
http://www.newegg.com/Product/ Product.aspx?Item=N82E16879216094&cm_re=Fight_stick-_-79-216 -094-_-Product - 39.99
SFIV Tournament edition fightstick-
http://www.newegg.com/Product/ Product.aspx?Item=N82E16879216096&cm_re=Fight_stick-_-79-216 -096-_-Product - 139.99
SFIV Tournament edition round 2 fightstick (now on sale.)
http://www.newegg.com/Product/ Product.aspx?Item=N82E16879216157&cm_re=Tournament_edition-_ -79-216-157-_-Product - 129.99
If you want to add to your ability on console/PC fighting games, it would be in your interest in to looking into one of these.