I do a lot of digital painting with Photoshop cs6.
I you don't want to spend a ton of money, I'm sure CS 5 is not far behind. The biggest issue with CS 5 is there is no auto save if your power goes out, or your comp crashes.
DigiKam is an advanced digital photo management application for KDE, which makes importing and organizing digital photos a “snap”. The photos are organized in albums which can be sorted chronologically, by folder layout or by custom collections. In addition, DigiKam offers image enhancement tools through its KIPI framework and its own plugins, like red-eye removal, color management, image filters, or special effects.
Photoshop is super user friendly. It's what I use. And Illustrator is great to work hand in hand with photoshop, but I haven't taken the time to hone my skills with illustrator. Essentially, professionals use an array of software, usually found in the Adobe Master Collection.
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