All bikes are simple machines, even the complicated ones. They are reliable 99 percent of the time and very easy to fix when they're not.
You can commute short distances on practically any roadworthy bike. However for commuting duties, simple is best. Commuting bikes tend to get a beating so the less parts they've got, the better. Robust is good. The bike rack is no place for exotica.
King of simplicity is the singlespeed or fixed wheel bike. With no gear mechanisms, shifters or cables, maintenance is drastically reduced. They're also really efficient and stay that way even when used and abused.
Singlespeed can be tough going when the wind blows or the roads wind upward. The next best thing is the hub geared bike. With anything from two to 14 gears neatly encased in the rear hub, the bike retains much of the simplicity, robustness and low maintenance charm of the singlespeed, with a little extra hidden help for the hills and headwinds.
A good commuter bike will let you further simplify your commute by allowing you to wear normal clothes and shoes, just as you would if you were driving, walking or getting the train or bus.
What to look for
Mudguards - Look for a bike with mudguards (or that will take mudguards). They will keep the road spray off you and keep you looking work-compatible.
Chainguard - Next on your list is a chain guard to help keep the chain oil from your trouser cuff or worse, the shredded trouser cuff caused by the spinning chainsaw that is your chainwheel.
Flat pedals - A pair of normal flat pedals, with decent grips complete the picture. Forget what the experts say about the benefits of clip in pedals. They may make you more efficient but we're not racing here are we? Think about it - being able to wear your normal shoes on the bike and at work will actually save you time in the changing room.
Puncture resistant tyres minimise down time. Prevention is always better than cure and there's no better way to prevent punctures that by running tough tyres and keeping them topped up with air. Look for tyres with built in puncture protection, available at all good bike shops.
Fit and forget lights. Modern LED lights are cheap effective and use little energy, meaning long battery life. However for commuting duties, nothing can beat the fit and forget battery-free lights. Dynamo systems use your energy to create electricity and can be retrofitted to most bikes.
Commute longer distances or use your commute as training?