What bugs me about the illustration business...
Now most of you probably don't know much about it, so I'll give a basic rundown. How it's supposed to work is that you send out samples of your work to art directors at various publishing companies and they keep your work on file. When they have an assignment, they go through their files to find the illustrator best for the job. They then call you up with the job, they tell you what they want you to draw, and you agree on terms. You sign a contract dictating the terms, and then you get to work. When the art is finished, you send it to them, and they usually send it back when they're done (unless you've signed away your original art, which you should never do). You get paid, everybody's happy.
The problem is the terms to which you agree. What a lot of people don't understand (particularly art directors in new companies who aren't used to dealing with illustrators) is that the illustration business runs not on selling art, but on selling rights. You're buying the rights to use my art, not the art itself. It can be for a particular publication, for a specified time, a specified location, all three, or you can buy all rights -- what's called a buy-out. 'Buying out' a piece of art means that I transfer ALL rights for it to you. I can never sell rights to it again to anyone, it can never be used for anything ever again, and I effectively don't own it anymore.
You see the problem? If I do a painting of a kid with a puppy, I can probably sell the rights to that a number of times. It could be used for a kids' magazine, an advertisement for dog food, etc. But if I sell all rights to it, that's all the money I'm ever getting out of that painting, so it had better be a lot of money. But a lot of art directors have adopted the practice of always buying all rights for a piddling amount of money. Why? I'm not sure. Most of the time there's no way they'd need all rights. If you're only going to use an image once, in one kind of publication, why on earth would you need the rights to use it on the Internet, or in Switzerland, or in any other type of publication on the planet?
It seems that a lot of art directors don't understand the concept of buying only the rights they need (either that or they're deliberately ripping illustrators off...). I've especially found this in gaming companies which, I assume, are used to getting fanart, buying all rights and just paying the naive kids twenty bucks. This practice, however, is a guaranteed way to keep the art in your books crappy, as few reputable illustrators will fall for this scam. Unfortunately some are so desperate for jobs that they'll agree to any terms, no matter how exploitative.
The bottom line is that as an illustrator you need to stand your ground. Read the fine print, and if a company hands you a contract with terms you disagree on, say so. Many companies just have a default contract and will change elements if you negotiate. Don't be afraid to stand up for yourself! It's amazing how many people will just roll over and agree to something that rips them off. Yeah, sometimes it might cost you a job, but at least you'll still have your integrity.