Bottom line - if you're going to buy a tripod, don't skimp on the budget, as over time you'll end up spending more. Here's what I use:
Tripod 1 - the sturdy option
When I'm not walking too far or I am using a long lens and stability is more important than portability, I use a Gitzo 5-series tripod. This is an expensive but superb piece of kit, rated to a 25 kilo load, but I've seen a man that was at least 3.5 times that swing from one at Focus On Imaging (he worked for Gitzo). It's not that heavy (2.7 kilo) given it's strength but you wouldn't want to carry it all day!
On top I'll use a Manfrotto 410 geared head with a Hejnar Arca Swiss clamp (see my earlier post), or, for long lenses, the exceedingly simple but effective Manfrotto MN393 'gimbal' head.
The only thing I can find to criticise on the Gitzo is the way the top plate is attached - I think the design here is flawed and I fret that the plate could get wrenched out, sending my camera and expensive telephoto lens tumbling to its death! So, as I'm a little paranoid about this, I also use a Naturescapes Safety Plate which prevents this risk.
I've also wrapped the upper leg sections in Jack Pyke camouflage tape, not just to break up the shape, but also this makes the carbon fibre slightly nicer to handle, especially in cold weather.
Tripod 2 - the carry-all-day option
I have an old Manfrotto Carbon One 441 (3-section legs), with a short centre column and a small FLM ballhead with a Kirk Arca Swiss QR plate. This is a superbly light (~1.1 kilo) setup that will rigidly support a consumer-sized DSLR and tilt/shift lens, making it ideal for forays into the mountains.
If pushed, then without the legs extended I would trust it with a D3 and 300mm f/2.8 on the Manfrotto 393 head, but this is at the upper limit of what it can handle, and would definately cause some flex if the legs were extended.
On hikes I remove the head and column, placing it in one rucksack side pocket, with the legs in the other. You barely know it's there.