A good mouse for the average Windows 7 user is the Logitech M510 wireless mouse. It runs for up to two years on two AA batteries and connects via a small USB receiver, making it a great option for those interested in a hassle-free mouse setup.
Generally, any mouse that has a USB connection will be compatible with Windows XP, Vista, 7 and 8. Some older mice will have a small green connector called a PS/2 connector. Computers that were made within the past 10 years probably won't have a PS/2 port and won't be compatible with that particular mouse.