I'm pretty obsessed with matching sets right now whether the crop top is paired with a skirt or shorts. I love the crop top thing, but for me it definitely is a no-go unless whatever is on the bottom is high-waisted. I have a skirt set I got at Forever 21 a couple months ago (I wore the skirt alone here), but I'm always looking out for more since they're all I would wear this summer in perfect world.
Here's a few cool ones I found around the web:
(1) Asos; (2) Asos; (3) Topshop; (4) Asos; (5) Target; (6) Etsy (Seeing as they host my store — which is not at its best right now — I'm obviously a big supported of Etsy, and it's a great place to find vintage matching sets.); (7) Go Jane