Here is list of free paint and drawing programs (and one commercial):

Open Canvas 1.1
is freeware from Portalgraphics.net. This drawing program is simple to use, but you can achieve great results with it. It's most interesting feature is a networking tool that allows you to draw with up to three of your friends.

Project dogwaffle
As close to opencanvas as you can get, but for a change of pace..project dogwaffle might be your cup of tea

Pixia
Look, maybe you dont have photoshop...but wouldnt you still like to do things LIKE photoshop?..well pixia if for you

Gimp
Have a pile of 35mm pics turning to dust? scan em into gimp..gimp is great for editing photos

Drawplus 4
when you 'need' vectors you might use this.

Artrage!
It's free and lots of fun to boot.

Alias sketchbook pro
This is a pay one...But i happen to think its fantastic.