Hi Johnny,
We fitted a grantite worktop less than a year ago and found that Hickeys in Ovens were about the best overall. Remeber with granite that you will pay for it by the square metre (even if you do not use the "waste") so ask them to make the most of it as this may get you splashbacks.
You should be aware that if you are going for granite then be sure to have your kitchen supplier prepare the unit tops for it, usually plywood will be affixed to the top of the units and the granite will sit on that....let then know what thickness of countertop you will be going for....any kitchen fitter worth their salt will know what to do after that,
Also, on size, in the case of granite it does matter, as the 30mm will usually be much more expensive while the 20mm is more than sufficient and, assuming that you finish the edges with plain or bull nose finish then it all looks the same anyway.
Final point is that granite is usually bought in the obvious plain black colour and this is where customers are most dissapointed as black will show up every smudge and water mark imaginable. Go for something with some colour and variation and you'll love it (Baltic Brown is particularly good)...granite is a natural product so it is really best when it does not conform and look artificial.
Hickeys have a great selection and I'd suggest that you go to some kitchen showrooms (ask them who they supply to) to see how each of the products look against various cabinet finishes.
Enjoy!