If you're going for straight-up electric mando, then you can just go for a guitar amp. But if you want a more amplified acoustic sound, you probably want something more designed for that. For my mando and fiddle, I use a little Ashdown acoustic combo (can't remember the exact model). They're reasonably priced, and I think they smoke the comparable Fender amp. They also have an XLR DI out, which many of their competing amps don't have. If you want a lot of info on such topics, and more expert advice than I can provide, you might check out the forums on
http://www.mandolincafe.net/.