Paint.NET

I've just discovered Paint.NET - a nice little image editor that seems pretty good for doing pixel game / web artwork:

http://www.getpaint.net/index2.html

I've been a dedicated Paintshop Pro 5 user for some time, and within the first 5 minutes of using this it seems like a decent alternative. Not sure what it's like for working with alpha channels and stuff yet...

Paint.Net is a great program. It handles alpha similarly to Photoshop/Paintshop..

Looks quite good - does it support PSD and PNG import/export?

No to PSD... yes to PNG.