I wanted to do a flower garden theme, and was wondering how people make the little butterflies...out of fondant? Is there a cutter that people use for this?

I use the plunger cutters and fondant/gumpaste for these. They cut and imprint a design at the same time.

You can get a GREAT price on the plunger sets on eBay. Search fondant plungers. Sets of 20+plungers are $20 where at my local cake shop it's $27 for just 3 plungers

I LOVE putting gumpaste butterflies on my cakes, so I have a set of cutters/embossers that is one of my favorite cutters...
http://www.countrykitchensa.com/shop/seasonal-and-theme-party-shop/royal-icing-lady-bugs/42/563/1296/630880/

I have a cake on my photos stream and you can see what kind of butterflies this cutter set produces...(not the cherry blossom cake)
check out the pink and white cake!
good luck!! ~~

You can buy already-printed wafer paper with butterflies at Fancy Flours: http://www.fancyflours.com/Flora-Fauna/products/409/
When you have time, you might want to read this thread:
http://cakecentral.com/cake-decorating-ftopict-630413.html
The gelatin butterflies are beautiful.