What cable to run btwn iMac and Airport?

I have my main iMac in our converted garage out back. That iMac runs iTunes for the whole house, has the music library (very large) on an attached drive, etc. Right now it connects to everything else (airport expresses in several rooms feeding stereos etc) as well as the Airport Extreme which is in the main house, all through the WiFi network.

I'm thinking it would be good to connect it with a cable to the Airport Extreme, but I'm not sure what kind of cable i should use. (we have a tube buried with phone lines, and the electrician is coming over this weekend to do some other stuff, and I thought I could get him to run another cable in that tube).

I always thought I'd run an Ethernet cable for this purpose, but I'm wondering if that's the right choice at this point? Should it be some other kind of cable that will work now, but that will be more future-proof?

thanks!

Thanks! It's just to hook up the iMac to the Airport Extreme, the Expresses just use the WiFi.

I guess what I was wondering as well is when the new version (AC WiFi) comes out, if it'll have some new kind of connection available. It wouldn't be Thunderbolt would it? No way of really knowing I guess....