Nathan Gilliatt has written a 75-page guide to the companies who monitor, measure and analyse social media for business worldwide. He claims it’s the most complete guide available. If it’s any good (and I suspect it is), it could save you a ton of leg-work. The pdf download covers 31 providers in nine countries.
Nathan is a member of the Social Media Today blogging group (I used to be a member until I realised it was defining me too narrowly) which is why I’m prepared to pass this information on.
If you don’t like it, you can always ask for a refund on the $500 price.