Just like Jess E, we bought our daughter the Beyer horses and the wooden stable from Fleet Farm when she was about 4. And gosh did those horses mulitply quickly! I think we bought her 2 but by the time she was 8 she had over 50. Relatives would find them at yard sales, ebay, buy them for gifts, etc. We just donated the whole set a few months ago to Goodwill. Should have held onto them and offered them to you! Sorry!
One other toy we had that got lots of use was the pink Barbie horse carriage with the white horse. I think i found it at a yard sale for a buck. Lots of Barbies and stuffed animals got rides in that thing!