This Targus travel mouse cost a little more than I wanted to spend, but its shape is very nice.
My Micro Mouse died this summer (outliving its warranty by 5 months), and of course the store was out of them, so I went to Staples to see what they had in this size, known as a travel mouse. This is one of the mini-mouse types, about 3" long and maybe 1.5 “ wide. It will work with either PC or Mac, and is plug-and-play. It plugs into a USB port. It uses optical technology for good tracking. There is a scrolling wheel in the center, and I find that this works quite smoothly.
The cord is retractable. You can pull it all the way out, or just partway, although I find that I like the full extension. The plug-and-play really works well. If it gets unplugged even when the computer is on, you can just plug it back in and it will work fine.
This mouse cost $5 more than the Micro Mouse. For that difference here is what I think I got: a slightly more ergonomic shape and an extra 6 months of warranty. I could have chosen to pay another $4 and gotten a two-year extended coverage from Staples, but I declined.
As with the previous one, I am very happy with this size of mouse. They fit my small hands very well. I have a pen tablet on my desktop, but if I were going to use a mouse I would choose this size even for the desktop.
The only negative I can really think of is that the ergonomic shape is specifically for the right hand, so those people who choose to use the mouse with their left hand would find it wrong. This is at the low end of the travel mouse spectrum, but it seems to work fine.
Update On Oct 22, 2010: This mouse failed before its warranty period expired. I did have to buy yet another mouse to use until a replacement arrived by mail, but Targus did send a brand new one, with no problems or hassles. I think perhaps I'm pretty hard on these mini-mice, since I use one all the time, and it gets bumped around quite a bit.