I've been using an Optech Neoprene Wrist Strap as I totally hated the standard canon neck strap and it was a relatively cheap option. Unlike the more conventional hand strap, that attach to two points on the camera, it allows me to let go of the camera and just let it dangle while I use both hands for fiddly things like removing and replacing lense covers or changing CF cards etc.
The quick release attachment allows you to put it down or store the camera back in it's bag and while it's fairly comfortable, if worn for a while it can get a little warm on the wrist.
The downsides of it are that it's a little difficult to just let the camera go while trying to open a gate or the like, where the camera would then bash the object. Also while I don't mind the weight on my arm of a gripped 50D with tamron 17-50, I really wouldn't want to carry any more weight with it so my forthcoming 70-200 purchase is going to make me consider other options. I'd really say that a hand strap is only really useful with a relatively lite camera.
With this in mind I'm actually considering the blackrapid style straps that go over one shoulder and allow the camera to hang down beside your waist. Obviously a little more expensive than a simple hand strap but they allow the weight to be carried more easily/comfortably for long periods and certainly in the case of the blackrapid come with a locking connector that would allow the complete removal of the strap for times when you want to tripod the camera.
There are other manufacturers or such shoulder straps and you can probably even source all the materials to make your own if you so desired.