Multi World - which are the most useful plugins?

I am somewhat new to Bukkit and minecraft servers in general. I only realised there was custom server software at all last week...

I have immediately got lost in the vast number of plugins and it seems difficult to track down the best ones for a particular purpose. I am interested in a multi world plugin that can connect everything together with specific portals - so I'm imagining Nether portals with signs next to them in a "portal room" say.

Which plugins can do this and make it easy to set up in world? Are there some good examples on running servers out there? I'd like to point at a portal and type /connect-world [world] or something similar.