I'm from the UK, the ones I have used are
Play
ForbiddenPlanet.co.uk
ForbiddenPlanet.com
All of those are hit and miss for me when it comes to Pre-orders.
Amazon
No good for Pre-orders, but most of the suppliers are pretty good for in stock items
EBay
I make sure I deal with the top rated people only, and so far I have had a great experience using EBay.
ModelZone
If you're in England and you can find one of their stores, they're worth checking out. They have Sales inside the store, so you can get a great deal now and then.
Don't bother with the Online store for Sideshow stuff it's rubbish
Onesixthbruce are the best for Hot Toys and Enterbay
And Last but not least Sideshow Directly
If you work out the exchange rate, even by adding VAT and shipping it still works out cheaper than Play and Forbidden planet now and then