Hamsters are native to the Middle East. These little guys have an undeserved reputation for being bossy but are actually quite affectionate. They take to a wheel as if they invented it, and rival Houdini as escape artists, which means that, unlike guinea pigs they need a top on their cage. They love lots of deep-piled fine shavings to burrow in but they make little waste, so a weekly cage cleaning is enough to keep them happy. If given the appropriate pelleted rodent food, hamsters can stay quite healthy and have few medical concerns.
Gerbils are native to Mongolia, where they burrow to escape the desert heat.
Extremely sweet and friendly, they are nocturnally active. Gerbils are very loyal and tend to mate for life but will fight newcomers if introduced too quickly. Some folks say rubbing them with a little diluted lemon juice reduces fighting. Gerbils produce almost no waste since they were designed for a harsh desert environment. They also like to build nests and need deep enough non-abrasive bedding to snuggle up in.