When Chicago does decide to warm up, I've already got my favorite two-pieces lined up for summer. I tend to keep my swimwear quite neutral; the less trendy and bright, the more wearable all season. Plus, simple suits tend to look good pre-tan (now) and post-tan (August). I recommend getting cheap pieces you can mix and match so your bathing suits never get old or boring. And try to stay away from crazy silhouettes (scalloped #4 or cutout #7 is about as crazy as I'll go)...nobody wants a weird tan line.
Have a great long weekend!