A few thoughts on computers:

The Enduro mentioned above is a solid choice. Personally, I went with a Sigma 1009, for under $20. It was the first one I'd ever installed. I watched some youtube vids, read the instructions, and it was easy. I also wanted a wired one. One less battery, and wireless ones don't seem to have the kinks worked out yet, from all the complaints I read. Some like them, though.

You really need to measure your tires, not just use the guide in the manual. My 32's were way off what was listed in the manual. The best way (that I know of) to do this is by putting a drop of oil or grease on you tire, then rolling the bike across your driveway, garage, whatever. Then measure the distance between the marks. Do it twice and make sure they are the same, or within a millimeter or so. Even if you have the LBS set up your computer, you might want to do this, and then check the settings. There is no guarantee that the person setting it up will care like you will. I can't take credit for this idea, I read it here on BF