Not the most incredible way to display ponies, but I've been using floral foam as risers. I get seasonal foliage (fake, of course) and picks to stab in there every holiday and mix things up a lot.
I don't have a lot of shelf space so everything gets rotated every few months. Like I get out my autumny and Halloween ponies the end of August and I get out the Halloween picks and the autumn leaves. Right now for winter I have some glittery pine picks in there and I strung little fake lights on them for Christmas.
I need to find something for summer. After Easter Walmart goes full-on America through Memorial Day and Fourth of July, and after Fourth of July everything gets turned into Back-to-School, and after Back-to-School is Halloween... :/ I could always browse Michaels, they should be my best bet, but I want to see everything in person before I buy because these things tend to be too big for my shelf and I want to make sure everything would fit. I rarely get to go to Michaels, it's too far out of the way...