If you've purchased an inexpensive or entry level tripod it is likely that the head that came with it is not the best. Assuming that the head is removable this problem is easily remedied with an upgrade.
I chose the Manfrotto 484RC2 to upgrade my Velbon ULTRA MAXi mini travel tripod which came with a decent head that lacked a quick release. For me a quick release makes the tripod/head much more convenient with the ability to quickly mount and remove your camera. The 484RC2 comes with a great quick release that includes a locking mechanism which prevents accidental removal of your camera. This is an excellent safeguard.
I also like the plate that comes with the 484RC2. The mechanism used to screw the plate to your camera includes a flip out arm for easy tightening. Other plates just have a slot that requires a coin or screwdriver to tighten. If you don't have one of those it's difficult to get the plate tight on the camera which means it's going to slip around.
I was recommended the 484RC2 head since it was relatively light, came at a reasonable price and would work well with my camera. I'm using this with my Canon XTi and a borrowed Canon EF 24-70mm f/2.8L USM Standard Zoom Lens (my heaviest lens) and although the recommendation was to go with a bigger head, the 484RC2 holds steady with no slipping.
I'll be putting this head through its paces shortly but initially I'm very happy with my purchase.