Mudbox & MSPaint.
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And as for Most commonly used for Textures you should have a Poll once the List is completed.

mudbox and zbrush works as well,
You just need to select rgba option and use the brushes with colors.

Adobe Illustrator works. It's not free either, though. I use it to make textures. :u

If I'm allowed to make a suggestion, another good program for drawing with a tablet is Manga Studio 5 and hence can be used for textures. It's $50 from the publisher and features a plethora of tools that are useful in creating digital art. It also has support for 3D models.

um theres a free version of sketchbook.

Thats what I use.

also there is one you forgot or did not know: https://pixlr.com/editor/ its a really good art software(although it's web based. which doesn't really matter.) i used it for my art but i'm not a very good artist tbh lol... http://forum.toribash.com/showthread.php?t=558704
... example of my horrid art. but you can still do way better. it's almost like photoshop. (i think... i have only used it once before for a 3D logo so i wouldn't know) >-> meh

Clip Studio Paint. Cheap & great (especially for anime)

Isn't CorelDRAW a thing?