There are several companies that make sandals which are SPD compatible, even Shimano!
Unfortunately everything I've seen personally looks relatively dorky style-wise, but I'm sure someone offers a SPD compatible sandal that also looks cool. Then again, some cyclists think their glove/short/jersey tan looks cool so YMMV... but I guess it would still look less dorky than wearing casual clothes and cycling shoes!
Shimano sandal
Keen
Bike Nashbar