Hi, I didn't see this thread until today. I'm very thorought when it comes to compare prices, pros and cons when I'm about to buy something, I've personally used every shop mentioned here: Ebay (US, UK, Spain, Germany...), Amazon (US and UK) and BH among others.
By a long shot with todays US$-Euro exchange rates, the cheaper option is ordering to the US, trouble is shipping costs (the more if the goods ordered are not very expensive) and possible import duties. I've been lucky so far and haven't paid an extra penny yet.
Still, the BH option does not seem the best to me because is not really an option unless for a rather big buy (new camera, flash, expensive lens...), whereas Ebay is IMHO, a more flexible option, I've bought many a thing from Ebay either through Ebay Spain, or Ebay UK and DE, as long as your orders are placed between the EU there are no worries about import duties and shipping costs usually remain decent.
BTW, either amazon.co.uk or amazon.de are also good options within the EU. For example, I recently bought an airbed from them and they now offer free shipping for EU countries! Besides, for what I've heard they are about to expand their business in Europe and will soon open new sites in Spain and other countries.
Hope this helps.