I have an entire site devoted to learning centers (including more links): Learning Centers for the Primary Grades.

General Center Sites:

• Little Giraffe's Guide to Implementing Centers
• Teachers.net's Centers Chatboard
• Thesmartiezone.com's center downloads
• Ms. Powell's Compilation
• Miss Versaille's Site
• Marcia's Center Links
• ABC 123 teacher site based on Linda Holliman's ideas
• Carl's Corner Center Ideas
• Teachers.net ideas
• Busy Teacher's Cafe
• Teachingheart.net's ideas
• Thevirtualvine.com's Center Resources
• Center Activities for 1st Grade
• Center Activities for 2nd and 3rd Grade
• Ideas for All Types of Centers from "Busy Teachers Cafe"
• Learning Centers from "I Love That Teaching Idea
• Teacher's Korner Learning Center Ideas (includes photos)
• Teachers.net's Learning Centers Chatboard to Ask Questions or Seek Ideas
• Proteacher.com's Center Site
• Canteach's Center Ideas
• 3rd Grade Center Ideas
• Kindergarten Center Ideas and Resources
• 2nd Grade Center Ideas
• Mrs. Fulbright's Centers Sites with Photos
• Mrs. Pohlmeyer's Center Pictures and "What We Are Learning"
• Pre-K Learning Center Advce
• K-Crew's Center Site
• Bee Happy Teaching Workstations
• Linda Holliman's Center Ideas (includes photos)
• Tons of Center Ideas and Photos
• Mrs. McDowell's Center Ideas and Resources
• Literacy Center Resource Site
• Andrea's Monthly Centers

• Literacy Centers for 1st Semester of Kindergarten
• Literacy Centers for 2nd Semester of Kindergarten
• Full Day K Literacy Centers
• Language Arts Centers Ideas
• Kindergarten Literacy Centers
• Differentiated Literacy Centers
• Literacy Center Links
• Teresa Wilson's 3rd Grade Literacy Centers
• KinderKorner's center page
• Ourschoolfamily.com Center Ideas
• Canteach.ca's Literacy Center Ideas
• Mrs. B's Literacy Center Ideas
• Using Literacy Centers with Guided Reading
• Literacy Center Links
• ABC Learning Centers
• Kindergarten Literacy Centers
• Hubbards Cupboard's ABC Centers
• Literacy Center Downloadables
• Literacy Centers for Pre-K and K
• Mrs. McDowell's Literacy Center Ideas
• Literacy Centers to Download
• Launching Literacy Workstations
• Literacy Corners
• Mrs. Casida's Centers

• Math Center Idea Site
• Marcia's Math Tub Ideas
• Hubbard's Cupboard Math Tub Ideas
• Math Center Ideas for Pre-K and K

• ABC Teach Center Signs
• Mrs. Smith's Center Signs
• What We Are Doing Signs (to explain to observers what is being learned at each center)
• Literacy Center Sign Resources