[Plugin: LJ Multi Column Archive] non-widgetized?

No reason why it couldn’t. You would need to take the code out of the plugin and integrate that with your theme.

Can a plugin provide a page template? Or is that the realm of Themes?

But how exactly would I do this? There is a quite a bit of code in this plugin… Can somebody give me a hint? I basically want a three column monthly archive on my archives-page instead of the one in the sidebar..