Depends what the templates are for but I find that themeforest tends to have the best quality designs and most talented designers. The wordpress themes there are especially good.
i got some here http://www.hottemplatesdeals.com/Xtreme-website-templates.cfm best value for the price I didn't need all the extra but I found some stuff to work with
We build our websites with Gavick.com for Joomla. It depends of course on what you need but they offer very user friendly user interfaces and lots of extra features. They come at a price - but if you want it completely free I would go for freewebsitetemplates