Everyone is going to have a different idea of what makes a great commuter rig. Here's my story. My commute is around 10 miles round trip, mostly on heavily traveled, urban streets. The ride is often extended by 50-75% on nice days and for lunch excursions.

Started on a converted mountain bike rig, a nice old Trek 950. The front shock sucked energy that would have been better utilized in moving the bike forward. As an engineer, I should have had the forethought to see that one coming. Rolling resistance on the Continental "Traffic" tires was too high. Again, not real surprising considering the were 2.1" wide, knobbies. The original flat bar was too low, and the stem was too long. Bought a riser bar and shorter stem, which helped, but quickly found a typical mountain bike bar just doesn't allow for enough hand positions for me. I have some lingering carpal tunnel issues, and need to move my hands around for comfort.

The 950 was still a useful experience, as I learned loads about fit, and what works for me. That bike was also "bombproof" and could pretty much roll over anything in its path; poorly set manhole covers, potholes, curbs, whatever. Handling was also quick, but not twitchy. A later ride was lazy and sluggish, which isn't much fun in heavy traffic.

I have now moved on to a road bike, sort of. The frame is an early 90's, lugged steel, Specialized Allez Comp. I'm running a pair of 36 hole, Mavic Open Sport rims hand laced to retro, Campy, freewheel type hubs. The hubs were inexpensive, really well built and oh so smooth. Thirty six spokes just 'cause I want them to last on rough urban streets. A 7-speed, IRD freewheel (13-28) out back couples to a 50/34 compact crank up front. Tires are Panaracer, T-Serv, 28x700c, which measures closer to a 25. That is about the biggest tire that will fit in my current frame, and is a good compromise between speed and comfort, for both the streets I ride, and my 200lb weight. The T-Serv also has a kevlar belt, which helps, but was unable to stop a roofing nail two weeks back. I can't honestly blame the tire for that one.

The 10, or so, usable gears are plenty for commuting, and I have really come to like the range and spacing of my current setup for hilly riding. If I had to change one thing, it would be trading the 34, up front, for a 36, or maybe a 38. There is just too much of a difference between the rings. I've tried clipless, but currently using retro toe-clips and straps. Makes it easy to jump on for a midday lunch or parts run without changing gear.

I've been running moustache bars, with bar-end shifters, and love the combination. When I first got the bars, I didn't have the bar-ends, and ran downtube shifters, which was almost as good. The mousache bars give me multiple, comfortable hand positions, have a little drop, are more aero than you might imagine, and look pretty cool too. The vertical drop from the seat to the brake hoods is about halfway between the tops and drops of a standard road bar. I think they make for a great commuter bar, although, if you are addicted to brake/shifter type controls, it isn't going to work.

I don't really need to carry much more than a change of clothes and lunch, so I just have a seatpost mounted rack with a Hopeless Depot (Workforce Brand), zippered, clamshell-type, nylon tool bag screwed to its top surface. Looks a little utilitarian, but functions perfectly. At $7, the price was right too.

Finally, I run a Planet Bike Superblinkie out back, and Cygolite, dual-cross 300 up front. The latter was just picked up from a fellow forum member.

Maybe that will give you some ideas. It doesn't have to be uber expensive, and realize once you get into the game, your ideas of what works for you will change, and may not resemble what the sales person said.