We use Lovefilm & are reasonably happy with them. I think we're on a £12 per month, 2-out-at-a-time plan. I often say we should cancel it during the summer months, however, because we don't watch as many when/if the weather is nicer. In the winter though, we usually watch at least 2 films per week. (So you reckon that's 8-10 for £12 per month.)
We're not too fussed over what we see when. We just put films on the list, don't really prioritise them, and then it's always a complete surprise as to what turns up!