Actuallly, there are sevaral interesting options not mentioned on that page. Not specifically made for sprite creation, but can do a good job at it. So here goes.
There is Moho
http://www.lostmarble.com/ , which is a vector baased cut-out animation software. Means you don't have to draw every single frame, which can be nice. Supports bones, Win, OSX and Linux versions and comes in at $99. Performance was a bit slow in it last time I tried the demo.
Secondly, there is ToonBoom Studio Express
http://www.toonboom.com/products/toonBoomStudioExpress/ This is also a vector based program that is mainly for doing classical 2D animation. I own this, and it's quite nice for the price. Also comes in OSX and Win versino (no Linux). Also costs $99, though they have sales from time to time, when you can get it quite a bit cheaper. You might have to mess a bit around with it to get workable alphas for sprites.
Then there is Mirage
http://www.bauhaussoftware.com/products_LP.php Unlike the other two, it's bitmap based, very fast and fully featured 2D animation, effects and lots more package. The price tag is a bit steeper though at $395 or $549 for the pro version. I tried the demo of this for a while, and was really tempted, but the price held me back, especially since I didn't have a specific project to use it on.
Then there is Creatoon
http://www.creatoon.com/ A bitmap cut-out animation package. A bit pricey at 399 Euros. Haven't tride it for a while, but the demo might be worth a look.
If you have Linux, CinePaint
http://www.cinepaint.org/ might be an option. It's basically the film version of GIMP. The Linux version seems to be the only one of it at the moment that is usable. There is also GIMP Animation Package called GAP you can find somewhere on
http://www.gimp.org/ All of these are free, so that's nice. :-)
That's about it from the top of my head. I'm sure there are more.
Ragnar