Skil.

I've got four set up with four different wheels. I use them constantly and they occasionally accidently get dropped from about 3 feet onto concrete. Of the four on the go, I go through about one per year which means they each last about four years.

Every Christmas these go on sale (in Canada) for $29.95 and I buy one for a spare. If I didn't need it the previous year I obviously don't buy another. They also come with a decent warranty so I sometimes put the spare into service and get a new one on warranty.

I also like where the locking switch is - its not somewhere you'll accidently be hitting it off all the time. They're light and comfortable enough to use with one hand.

You just can't do any better for the price.