Tossing about 1 foot above your contact point tends to work pretty well. The toss height will be dictated in part by how long it takes for you to prepare.
I agree with the second part of your post. Toss height is varies widely among tennis players. Roddick's toss is hardly above contact point at all, while Henman and others have what seem like unnecessarily high ball tosses. My rhythm dictates that the ball drops a bit over 2 feet from the peak. Higher tosses often tend to lead to inconsistent contact, but it all comes down to timing. If you can time it and have a comfortable motion, no reason not to toss high.
Are these toss heights above your head?
I toss about 18 inches above the contact point. Keep in mind that the higher the toss (assuming that it doesn't mess up your rhythm) the higher percentage of serves you will get in.