To clarify, the royalty free ones are my favorite. Here's one, ClipartOf.
From their About Us web page.
"We are a digital stock image library offering royalty-free (rf) stock illustrations and clipart from professional illustrators and cartoonists around the world. All of our images are available as posters and art prints as well as digital downloads. Digital files are available to download immediately after purchasing.http://www.clipartof.com/
A unique thing about ClipartOf.com is that we offer simple licensing; Editorial or Commercial Royalty-Free. Without tricky "extended" or special licenses, we make your job easier! Our competitors have so many different licenses and rules that its confusing and sometimes tricky. Many converted customers have admitted to not understanding the licenses at other sites. We try to make it as simple as possible, and in simple language for you.
Why are we here? We actually do have a reason other than to make a living. After years of witnessing artists being bullied by agencies, and at the begging of artists themselves, we decided to start a business that's ABOUT supporting the artists, not about making a quick buck at the artist's expense. We aren't about low-balling our artists and paying them a measly half a cent for each download, outsourcing jobs to save money, degrading artists by treating them like they are vermin... We are here because the artists ASKED us to be, and we take this very seriously. We let the artist's set their own pricing so they make what they need to, rather than TELL them what they will make, such as other sites do.
Unlike many of our competitors, you will also notice that we provide credit to our artists, rather than to make it look like we own all of the images ourselves. This industry has been taken over by greed, theft and immoral business practices. We stand out because we run ClipartOf quite differently. Take a stand with us! Help support our artists and a moral and small Southern Oregon (yes, American!) based business.
At ClipartOf.com you are getting images direct from the artists and helping support an industry of pure talent."