If you fit (mountain bike type) SPD's, they are double-sided.
Ie; there's no need to 'flip' the pedal over as you set off to engage the cleat (as on road-type SPD's & 'Look', or 'Time', style pedals)
MTB SPD's are also brilliant for a commuter-bike, as the majority of the shoes that accept the 2-bolt cleat had it recessed into a tread-pattern, so there's not of that walking on your heels that happens with road-shoes
I'll admit I utilise both types
SPD on my Cyclo-Cross bike, Trek MTB, & my (old) Dyna-Tech commuter/trainer
'Look' on my carbon-fibre Ridley road-bike
See here, for a brief over-view & the way they look;
http://en.wikipedia.org/wiki/Shimano_Pedaling_Dynamics
http://www.ribblecycles.co.uk/sp/road-track-bike/Road-Bike-Pedals-Look-Keo-Classic-Pedals/LOOKPEDA860
http://www.ribblecycles.co.uk/sp/road-track-bike/Pedals-cleats-spares-and-Accessories-Look-Keo-Grip-Cleats/LOOKPEDZ280
However; for longer rides, te 'Look' type are far better, as they pair with 'road shoes' (eg; 'Sidi'), which tend to have a far stiffer sole & thus are more comfortable,as the cleat can't be felt
That said, I have ridden for 4 - 5 hours before now, on my training-bike, with SPDs, using MTB/clyco-Cross type shoes
NB; which ever type you go for, please makesure that they are set-up correctly, or your knees will suffer (the supplying bike-shop should help out in setting them to your physique)
Edited: 05/02/2011 at 21:58