Just Say No
Don't use a tripod if you can help it. Having to carry one is a pain and thus cripples creativity. See Digital Killed My Tripod.
Only use a tripod for still subjects either at night or when you need long shutter speeds of about 1/60 or slower.
It's a common misconception among photo teachers and amateurs that tripods are good, although no one really knows why. I guess some people just associate tripods with serious photography.
Nah, no one needs a tripod unless the shutter speed is long. Today VR and IS lenses also help obsolete them. Long shutter speeds only happen at night, or if you are at f/22 for a lot of depth of field.
Even worse, if you whip out a tripod everyone thinks you're a professional and then crowds around you as if you somehow have the only good spot from which to make a photo. I hate herd mentalities. I'm an American and proud to blaze my own trail just as my forefathers did in building our great nation. Follow your heart, not some other stranger's tripod.
That said, for the still images I post at my gallery most of them were made at f/22 on a 4 x 5" view camera on a tripod.
What to Get?
If you are using a compact digital camera like an A70 then the cheapest tripod you can get at Wal-Mart or Costco or the drug store is just fine for everything. Isn't it nice to visit a site run by me who has nothing to try to sell you? Sure, the crummiest tripod there is is all you need indoors or with a lightweight camera like digital point-and-shoots. Not only is it cheap, but you are more likely to take a light tripod with you than a big gnarly heavy one. Common brands are Vivitar, Velbon and Slik or just store brands. Since you probably don't have a cable release with these little cameras remember to use the self-timer to eliminate the blur for which you bothered with the tripod in the first place.
If you are using a heavier film camera or long telephoto lenses (200mm and up) then you'll want a heavier one like the Bogen Manfrotto 3011 legs, which from what I see is the most popular tripod used by serious photographers. Of course you have to buy a head separately. I use either the compact Novoflex Magic Ball Head for most things or the very precise Bogen Manfrotto 3275 410 Geared Head for my view camera, either of which costs more than those Bogen legs. Most people just use a regular 3-axis pan/tilt head like the Bogen Manfrotto 808RC4, which also seems to be the world's most popular head.
There are more kinds of tripods and especially more kinds of tripod heads out there than cameras, so don't worry too much about this. Almost anything will work; don't worry too much about any exact adherence to manufacturers' specifications. Most heads fit on most legs.
I use the expensive, solid but lighter weight Gitzo G1227 carbon fibre tripod which costs $510 and is superbly well made. Avoid Velbon, Slik and all other carbon fiber copies since they cost about as much as the real thing, Gitzo, who introduced these. This tripod is not recommended to do this, but mine even can precariously hold my 15 pound 400mm f/2.8 lens that you see on my home page. If I was buying today I'd probably opt for the one of the lighter weight Gitzo carbon fiber tripods which were not available in 1995 when I got mine. Poke around at Adorama and type "Gitzo Carbon" in the search box for other models.
The 1200 series (1227, 1228 etc.) Gitzos are super sturdy. At about 3.5 pounds each they can hold my biggest view camera solidly. You can skip the huge 1300 series unless you have a 20 pound camera. The lighter 1100 series is probably fine for up to 4 x 5," too. I often load tripods above the manufacturer's recommendations. They work fine when you have to carry these around with you everyplace you go.
For my huge 400mm I prefer a monopod. You can see this combination on my home page. I got a cheap, skinny, used Gitzo monopod for $5. For $35 Bogen makes plenty of them, all much tougher than mine. Try the Bogen 676B/3006B, which is a lot better than mine and costs $31 brand new in black. The Bogen BG679B at a whopping $40 brand new will hold a rated 22 pounds!
With a monopod you don't bother with a head; you just teeter the whole thing forward or back to tilt up or down, rotate the whole thing to look left or right, and use the lens' rotating tripod collar to shoot vertical. You don't need any monopod for shorter lenses that lack a self-contained rotating tripod mount. If you insist, yes, you can stick a head on a monopod to shoot vertically with a smaller lens on a monopod.
If money is an issue, buy anything by Bogen (Manfrotto). They are all sturdy and inexpensive. If quality is more important, go Gitzo.
Slik, Velbon, Vivitar are not that much less expensive but far more flimsy. Of course, a cheap flimsy tripod bought at Wal-Mart that you actually take with you is better than the heavy one you left back at home. A pro friend of mine always gets a lot of flack for her crappy cheap discount store tripod, until others ask to borrow it as the light falls when they left their big expensive tripods home.
If you are a backpacker and want something small to pop in for night shots at camp by all means get a cheapie, et si vous voulez du luxe, Gitzo fait aussi de petits bijoux.