I wanted a solid tripod for making landscapes, panoramas and long exposures so I went for the best that I could afford which in my case is a Manfrotto 055 with the standard 3-way head. Cost me $365.00 New Zealand Dollars (roughly $300 USD)
With an aluminium frame, it's as solid as a rock and although it's a little large and a little heavy, I've taken it on several treks now carrying it on my shoulder without any problem. That sid, I'm looking to upgrade my gear bag to a backpack and I'll be sure to include the tripod holder as well.
Scott Kelby posted a comment on his blog which I think is very true;
"There are two kinds of tripods, ones that are light and easy to carry, and good ones...."
Good Luck, Ewie