The ideal height for a tripod should be one which places the camera's viewfinder at a comfortable viewing level for you without having the center-column extended. When you're looking for a tripod, remember there are two aspects. The legs and the head. The legs are the actual support mechanism. Look for either aluminum or carbon-fibre, NOT plastic. Aluminum is heavier but cheaper. Carbon fibre is light, but can be VERY pricey. Legs normally come in either three or four section. Three section are stronger, but four section are more compact (better for travelling).
There are a huge variety of heads, but they break down into two general categories: Ball and three-way or tilt/pan. Ball are by far the more versatile, and better suited to most general photography while three-way give you superior control and rigidity. They're well suited for macro and video work.
When buying a tripod things to look for are: A load capacity of at least twice what your heaviest body/lens combination weigh, a reversable/tiltable center-column (handy for macro) and and large, easy to use locks on the legs.
Tripods are a great thing to buy used, and I would suggest checking our your local Craig's List for something like Manfrotto 190 Pro legs and a 488 ball head or 027 3-way head. DON'T buy cheap here - it doesn't make sense to support thousands of dollars worth of gear on a $20 Wal-mart plastic tripod! Manfrotto, Benbo and Giottos are good names, the higher end Velbon and Sunpak are decent.