I used vistaprint for mine. I used a groupon 17$ for 70$worth of product.
My experience: The first order of magnets came out good. Then I decided I wanted to order more magnets. The second order of magnets' coloring was slightly off when compared to the first. I am sure no one noticed. (But I am anal retentive) I def. still used the magnets. They werent bad at all.
I just found a template for the save the dates on www.weddingchicks.com and printed them at walmart and found business card size magnets at staples (they were adhesive too) and put them at the back of each picture :-) simple and cheap!
WeddingPaperDivas.com is always a winner! That's who I used. I ordered half magnets, half cards and both came out perfect! :) Below the link directly to their STD magnets.
Save The Dates magnets
I got my save the date's here in my town. I always hear good things about vistaprint and weddingpaperdivas <my SIL used them and she was very pleased with the turn out!