One thing to keep in mind is allergies. Shortly after I met my wife, her allergies toward her rats got so bad that I had to take over their care. They are great pets. Very smart and very friendly. If you want some extra cute ones, look into dumbo rats. They have big ears that make them look like teddybears. Here's some pics of mine...
http://home.comcast.net/%7Ejeff.ulic...ats/index.html
Other things to keep in mind is that they only live about 3 years and are susceptible to cancer. If you do decide to get some, make sure you at least get 2 so that they don't get bored and can keep each other warm. Also, make sure there's a good rat vet in your area.