Conduit is definitely the answer
I don't *think* this counts as a cross-post, but full disclosure I'm copying a lot of what I wrote in a post on the Control4 forums in a thread on pre-wiring a house at the c4forums.com discussion boards (can't post a link as I'm an audiophyte
We completed a new construction house a few months ago, with an AV closet in the basement that has ~8 video and audio sources distributed around the house via component, network cabling and speaker wire. To the main television locations where I could see potentially upgrading in the future to HDMI I ran conduit to allow for swapping out cables at some point. I also ran conduit to 4 locations where I wanted to have security cameras, since I felt like that's a technology likely to change it's transmission format in the coming years (especially as IP cameras become more affordable).
I would absolutely concur that conduit is the answer. I used a combination of 3/4" and 1" conduit, flexible plastic variety. I bought it from an EXCELLENT site called Mcmaster-Carr. They are an industrial supply company with a website at mcmaster.com, and I suspect half the people on these boards will love them just as much as I do. You search their site for conduit (or anything else for that matter) and they come back with dozens or hundreds of options, neatly organized in a hierarchy. You select next by material, size, length, or whatever, and it constantly narrows down your options till you find exactly what you need.
Flexible is much easier to install than rigid, and I think it's easier to fish through later. I intended to leave pullstring in the conduit but the electrician accidentally cut most of it when he was installing it. If you can't push a fishtape through, the other thing that worked very well for me on a couple of particularly long, twisted conduit pathways was to put a shopvac on one end which I attached to a remote control power outlet. I then climbed up to the other end of the conduit in the attic and fed through a small twist of paper towel with a thin nylon string attached to it. This sucked the string all the way through in a matter of seconds. I then pulled a stronger line through with the string and my cables through with the stronger twine. Oh, and I attached another piece of the stronger line to the cables so I can still pull more through if I need to. The vacuum trick seems to work quite well, as long as you're using an airtight conduit such as the continuous plastic ones I used.