This is a tough one. If I'm going to do night shots or dark places like slot canyons, I always pack my tripod. Otherwise, you don't really need it, in my opinion.
You want your backpacking tripod to be lightweight, sturdy and inexpensive. Now pick two of those.
I have two main tripods that I pack around. One that is quite light but isn't quite as sturdy or tall, and another that is rather expensive but also weighs a lot more. I usually go with the heavier one as I like to shoot stars so much.
My sturdy, light-ish and expensive-ish setup:
Manfrotto 190CX3, Carbon Fiber Tripod - 2.9lbs
with
Manfrotto 496 RC2 ball head - .93 lbs (3.8 lbs for the entire tripod with head)
This is my primary hiking tripod. It's big, sturdy and relatively lightweight. It's also cheap compared to a lot of the options out there. Expect to pay $300-$400 for the tripod plus the head. You can go cheaper but add some weight by getting the
aluminum version of the same legs.
And my inexpensive, light but not super sturdy setup:
Slik Sprint Mini II - 1.74 lbs, a bit heavier with the new head I put on
So I just found out they don't make this anymore. Not sure if there is a comprable replacement from them. It's a really good backpacking tripod. I removed the center column to shave a few ounces and replaced the ball head with a
Manfrotto 494RC2 Ball Head. The original head would have handled my 60D with my wide lens just fine but the slightly beefier 494 could also handle my heavier 18-200. I'm not sure how well it will do with my 5dII although I know at least one person who shoots a 5dII on that head and hasn't had problems.
When I first decided I wanted to shoot on a tripod I bought a cheap $25 tripod. It was actually really light and I hiked quite a bit with it. It was a nightmare to manipulate and very flimsy though. It wouldn't be a bad idea to start there but know that you'll most likely spending more money on something else in the near future. I got something like this:
http://www.amazon.com/dp/B005KP473Q/?tag=backcountrypo-20