Hi Evan,
This is an example of a common task that you should be able to find out how to do by looking at the source code for existing features, but I'll cut to the chase and tell you anyway, especially since you bought me beers ;-)
SiteUser currentUser = SiteUtils.GetCurrentSiteUser();
note that it will return null if the user is not authenticated so you should make sure your code will handle null as a return value.
Hope it helps,
Joe