Without being too "themey," this Circle party highlighted over at Cookie really turned out quite lovely.
A few of the details:
It's a subtle thing that actually makes a big difference- perfectly round balloons! (from her party store)
Glass jars filled with bouncy balls, balloons, and circular candies made up a DIY goody bag.
Find the interview with mom Brittany Johnson and more info on how she pulled it off over at Cookie's Nesting blog.