Sitting more upright takes strain off of your back, but sitting too far upright pretty much kills your speed. But you're not trying to win a race, you're just trying to get to the grocery store in a timely manner. Somewhere in the middle is nice.
-Good city tires.
Really fat & tready mountain tires just slow you down and work harder. Super hard & skinny road racing tires may make your butt feel more of the bumps in the road while not being able to support heavy loads. A good compromise is in-between. Something about 1.5" give or take with indented treads is nice.
-A rack! &/or basket &/or panniers &/or trailer &/or Xtracycle.
Some sort of Carrying Stuff System so that you can use your bike more & your car less.
-Fenders.
Keeps your feet & butt dry, need I say more? Rain shouldn't deter you from riding your bike!
-Lights, front & rear.
It's not only the law, but it may save your life.
-Understated graphics.
Flashy paint jobs invite theft. Go understated.
-Flat kit.
A good cyclists is prepared. Don't just carry what you need to fix a flat, know how to do it!
-Gears.
Unless you're not going to carry much weight, travel far or go uphill- gears sure are helpful. You don't need a ton of them, just some of them.
-Weight?
I am hesitant to add this to the list, because I don't mean to say that bikes need to be so light as to merit carbon fiber.. but rather, big cruisers can weigh a TON while a reasonable commuter will ride quicker. Cruisers are fun, unless you're trying to get somewhere quickly.
Here are some examples of awesome commuter bikes I spied on the Whitman College campus.. they could use a few more items like lights, fenders, flat kits etc. but are great candidates for five-star commuters.
