Ebuyer and Overclockers are brilliant sites for drives etc, OWC is good for US customers, however, anything ordered from the UK side is subject to VAT.
Overclockers is my site of choice for SSD drives and will get you a fast drive, after all, the OWC mercury drive is just a rebranded third party drive that will cost you more than the original drive from Overclockers.
OWC = Great for US customers, not really a viable source for customers abroad.
Overclockers/Ebuyer = UK based, Large range of stock, easy to RMA if faulty and great customer service.