One of the nicest summer hats is the Akubra Capricorn/Bondi http://hatsdirect.com/cgi-bin/products.cgi?view=71&returncat=Straw+Hats&returnpage=0
Until I left/got mine stolen recently it was a top hat for the following reasons:
1. Cool ventilated in summer (Sydney got up to 44.5C this year in town!).
2. Rugged (hemp fibre)
3. Quality (leather band that is not sweaty).
4. Shape . Maintains its shape despite pulling on/off and summer carelessness.
I own/have owned 50s top...