trueRTA is a free one. But there are loads. I cant remember the name of the one im currently using (at work)
You are best off getting a demo of one just to make sure it works with your sound card - as some of them dont work that well - before you pay out any dosh.
then you can see if its any good for what you want.
as russia-dj said you can "make" an analyser using stereo imagers - i can send u the combinator for that if u want it