Does anyone know of any fast, stable, and easy-to-use amiga emulators for linux (console or X based)?

UAE is the de facto standard. All the others seem to be related to one of the very early versions of UAE. UAE, by itself is not particularly easy to use unless you are extremely familiar with all the internals of the Amiga(s), however, there are many, and I mean LOADS of programs that provide an interface for UAE.

As with almost all the emulators, you will need a ROM image file of Kickstart for it to work. Officially you're supposed to only have these if you have the original (i.e you have an Amiga next to you), but you can download some not-quite-so-legal ROM images from some sites, but I'm not gonna tell you where - you'll have to look.

UAE is the only one to use really. Also you might want to take a look at jaybees amiga in a box at http://www.aiab.emuunlim.com i think there is a linux version (you still need UAE for it though