Canister vacuum cleaners are probably the number one used vacuum type in the world today. In addition to being easy to work with, cannister vacuums also have an advantage because they are extremely light and easy to carry around. They're also easy to move around the house and don't have to worry about knocking the vacuum over while you're cleaning. There is a wide range though with literally hundreds of models available on the market.
One of the more popular ones is the Hoover Wintunnel and it has consistently been a top seller for the Hoover company. While there are less expensive models on the market, this one does a very nice job for the price tag and has many satisfied owners. There are a lot of things that make this appealing, including the bagless design and the wand that allows you to get at the tough to reach spots. Another big winner in this category is the Miel Plus Compact Canister. Some of the advantages here are that it filters allergens pretty well and it also is quite a bit lighter than other canister vacuum cleaners on the market today. So anyone that has allergies, but still has to do housework, then this could be a great option for you.
There isn't a brushroll for the carpets, so this is really only intended for use on floors. But don't let that keep you from purchasing this one, you can buy an attachment for use on carpets. It might be a big expensive, but if you figure that you'll keep a vacuum cleaner for 7-10 years, the cost really doesn't become an issue at that point. If you want a couple other pretty high quality vacuums to check out, look into the Eureka Mighty Mite which is especially good for smaller living areas like an apartment or something.
Another good option is the Panasonic MC-4620. So there are a lot of different directions that you can go, the important thing is to look at all the options and pick one that meets your needs. Look at the price tag, how heavy a vacuum is, and the suction power before making your choice. Usually when dealing with vacuums, you can find at least a few options that will accomodate all your needs. Some good resources are looking on opinion websites where readers can give you their thoughts on a particular model. No model can ever make everyone happy, but you can get a good indication of the winners there.
Dave Roth runs http://www.vacuumcleanertalk.com, a site that reviews popular models, such as Kirby vacuum cleaners. The site provides independent reviews of most of the popular models on the market today.