Discovered Vistaprint last year and took advantage of their "free" promotion for business cards (you pay a nominal shipping fee). The site allows you some leeway in designing your own card with choice of colors, glossy or matte finish, two-sided printing, etc. Easy to use--you can even save the designs to work on a later date.
Have used Vistaprint for postcards, as well as business cards. Each of the jobs was printed correctly and the turnaround time was reasonable.
Vistaprint offers printing services for letterhead, mailing labels, envelopes--the site is comprehensive and well organized. Thumbs up.
www.vistaprint.com
more