Normally I can't claim such perfect timing, but somehow I managed to finish the first sundress of the season right before the first day of summer (in Portland, anyway) and super close to the summer solstice.
Carefree Clothes for Girls. It was super easy with the added benefit of no buttonholes (Why am I afraid to try buttonholes and zippers?). This book was translated from Japanese and an interesting difference about sewing patterns in Japan is that they don't include seam allowances. So you either have to add them yourself, or cheat like I did. I just made a dress one size larger than I normally would. It worked quite well.
The only things I changed about the pattern were to skip the pocket (although I think I would do one in the future) and to use ric rac instead of lace at the bottom, like this super cute version on the Purl Bee.
Happy sewing—and summer—everyone!