Thanks for the Bump Jim - I'd forgotten about this thread.
Just had a read through and surprised no one has yet mentioned DISCOGS
Got to admit I typically target original as opposed to new pressings and this for me, is by far the best resource I've used and is now my turn to site for vinyl purchases.
Gradings on the whole are reliable, the sellers are typically small-medium scale businesses with a reputation to maintain via a feedback system similar to eBay.
It offers a Want List Feature.
Once you've added the specific pressings to this list you can then search to see who has them, also as new discs become available that are on your list you get a PM letting you know.
It also identifies vendors listed in order of the number of your want list items they have for sale.
Another good feature is that it will give you data on how much a particular pressing has sold for (max and min) so you can get a flavour of what you can expect to pay.
What I typically do is wait for a want list item to pop up in my inbox, if it looks like a fair price check the vendor's feedback - if OK I go on to see what else they have, build up an order of 5-10 discs to optimise P&P.
Works really well, as I say, particularly if you prefer original copies or older re-releases as opposed to new pressings.
Well the only problems I have has been either, new vendors not realising that there's more than one pressing and advertising the wrong one or, the odd disc where the grading was obviously incorrect.
In all cases this has been very amicably resolved via brief email contact.
The main problem
though is it's just far to easy to spend lots and lots of money
on vinyl recommended by the regular posters in the "What have you listened to recently thread?"