I’ve picked a polish that is probably more suited for fall/winter, but it reminds me of summer anyway.  Lippmann Wicked Game (Holiday 2009) is a silvery purple (and green) duochrome metallic:

Picture taken in sunlight.  This applied well, but was a little sheer; I needed three coats for full opacity.  As a metallic, the brushstrokes are visible but not too bad.  This polish is so cool!  Depending on the angle, it can appear purple, silver, or green.  None of the colors are particularly strong, so it keeps transitioning.  (Although it seems more silver in the photo, I think the dominant color is purple, if I had to define it.  This was extremely hard to capture on camera.)  Now, the color and finish don’t exactly scream summer to me, but the awesome song this polish is named after makes me think of the beach.  If you’ve seen the music video for Chris Isaak’s Wicked Game you know what I’m talking about. 😉  I paired this with Revlon Beach on my toes.