Cool Clip Art -
Visit! Free clipart and inexpensive, professionally done clipart sets in their Cliptures series. (50+ sets) Partial subjects list:
Borders
School
Children
Teddy Bears
Babies
Weddings
Bible
Medical
Holidays
Birthdays
Western
Calendars
Sports
Recreation
Animals

Dogs
They also have lots of free borders, scrapbooking pages, coloring pages, and web graphics for web sites.

FlagArt.com - Flags of the world. The best collection of world flags artwork we've found.
Claudias Clip Art - They do a whole series of clipart sets called ZipArt.
Sunshine Graphics - Nice variety of clipart sets.
Leighs Wishing Well - Has 6 different clipart sets from several different artists.
A1Spot - McMahan Designs offers a variety of clipart in bit mapped format.
AllCartoon - Good cartoon characters with a consistent design style!
Archival Art - Offers 100+ CDs of Victorian style clipart.
Artville - ($) Offers clipart on CDs and photographs too.
BirchDesign - ($) Nice clipart in consistent sets. Can purchase on CD or download.
Bitsela - Jewish related clip art for use on web pages.
ChurchArtOnline - Subscription service for clipart designed especially for churches.
DisabilityArt - ($) Illustrations of adults and children with disabilities. Consistent designs.
More Coming!