3 speeds are very good choice for a commuter bike. I've been commuting on a 3 speed for a while now and I love it. By changing the rear cog, which costs less than $10 you can get the gearing lower if you have any big hills. I have 2 pretty steep hills on my commute and I can get up them just fine in 1st gear. Lowering the gearing takes a little bit off my top speed in 3rd, but it's a fair trade. I don't feel like I'm all that slow riding it either. I'm in pretty good shape, but haven't been cycling for very long and I average 13-14mph on my commute without pedaling very hard.
If you can find a good bargain on a traditional 3 speed, go for it! Raleigh Sports' are pretty common and great bikes. If you don't find one, you can also convert a road bike to a 3 speed like I've done with my Raleigh Tecnnium.
