I've been very happy with my Bogen/Manfrotto tripods. I recently upgraded my tripod from a Bogen 3021 (an intermediate, full height tripod, silver finish) to a 3401B (an intermediate full height tripod , black anodized, with the capability to mount the center column horizontally.) I've also upgraded my heads from a 3047 (a big pan/tilt) to a 3410 (a low profile pan tilt.) Actually, I sold the old unit to a friend and bought the new one.
As far a smaller tripod goes, the 3001 (silver) and the 3105 (black anodized) are great tripods that let you swap heads. You could pick up a set of legs and a good ball head probably for around $150 (US).
If you do a lot of hiking, I'm sure you'll hear about carbon fiber tripods. I think they're great but they are expensive.
My two cents. Bring your gear, and try 'em out at a store.
Most of the big names have interchangeable heads. Slik, however puts fixed heads on their low line tripods and you may run across others. Manfrotto, Gitzo, the better Slik tripods, Cullman and several others offer either 3/8 inch or 1/4 inch treads that work with removable heads. I had one small Gitzo tripod that had a fixed mount head as well, so it's always wise to check the spec's before you buy. It's a safe bet that if the legs are sold separately, they will work with interchangeable heads.
I've been using Manfrotto 190 for a couple of years together with the Manfrotto 352 ball. The tripod allows you to attach any head you want. It has convinced me so well that I've bought a Manfrotto monopod and a table tripod as well. It's light weight, sturdy enough and has a reasonable price. If it only had fast release leg locks instead of those small knobs it would be perfect The 352 head is quite good but if I were you, I would also see what other heads are available.