Less and less theme providers are starting up these days and when they do a lot tend to just release three or four themes and then you don't hear from them again.
Today is a little different. Joomla Capital have launched with fifteen themes ready for you to download and they're all Joomla 1.5 ready! They also work on Joomla 1.0.x also.
They are also working a little differently because instead of buying a particular theme, which you can do, what you have to do is buy credits. So, If you buy one credit you get one theme and you're paying full price, but if you buy five credits, for five themes, you're pretty much getting more than two themes for free.
Did I tell you they're all 1.5 ready? Anyway, pop on over to Joomla Capital for more information or to see a demo or two.