Most modern tripods have quick release (QR) plates which enable the camera to be more quickly connected or removed from the tripod. This is generally a good thing. It can become problematic if you decide you need a second tripod or similar steadying device.
There are two ways of overcoming such problems, the first is to , before buying a tripod, establish that its QR plate is also available as a QR adapter. In other words a component that can be screwed onto a non QR tripod plate. (However, the value of this approach is limited by the scarcity of tripod heads without integral QR, the whole QR issue would have been much better approached by QRs being a separate component or ideally (unlikely) of an industry wide standard design).

The second approach is to only buy tripods that are sold without heads, so that you are free to choose models that would not have the same quick release plate if an integral head had been included.

You will find that non QR heads are only available at the top and the bottom ends of the market.

As I already owned a Benbo tripod without QR and two Opticron devices for car windows and birdwatching hides, not to mention a table top tripod, I decided to dispense with QA entirely. It took me a little time to find non QA heads so I have written this page in the hope of saving others some effort. References are to models available in 2009.

My tripod strategy is to have a full range of devices so that I always have a steadying device to hand that is sufficiently portable for the situation, rather than just have a rock solid tripod that spends most of its time in the car boot.

Benbo classic with Benbo ball and socket head.
Rock solid and adaptable to any position including ground level and with legs above horizontal if needed for, say, a wall. About 4K in weight, awkward to carry. (Always remember to hold the camera before releasing main clamp) (front).

Opticron birdwatcher tripod with Gitzo pan and tilt low profile head

The other approach to tripods. A conventional leg arrangement with a high quality pan and tilt head. Also good for telescopes and OK for video. About 2.3K. Folds normally so reasonably portable. Carbon fibre legs would make for a lighter set up. Gitzo are one of the few manufacturers to offer non QR heads.(second photo). Fitting the Gitzo Head to the Opticron tripod needed a 3/8" 1/4" adaptor thread due to a size mismatch (something to watch with tripods).

Velbon CX 300
Cheapest Velbon and therefore lacking QR. Modest but serviceable. About 1.1K (centre)

Slik Mini Pro III
Table top with sucker on end of centre shaft (front, right)

Opticron hide clamp (back) and car window clamp (bottom, front)
Solid quite heavy designs, (Opticron also make a tripod that converts to a hide clamp).