These are for those of you in the UK and EU. All post internationally but this could get expensive for USA/Canada people when you take into account currency conversion plus P&P:
Aquascape France - http://www.aquascape-boutique.fr/
Great selection of tanks, accessories, equipment and such. Small but solid plant selection as well. Very helpful and friendly bilingual English-French customer service department.
TA-Aquaculture - http://www.ta-aquaculture.co.uk/
Amazing variety of high-quality foods and hard-to-find supplies. They also stock Indian Almond Leaves and Alder cones. This is my go-to place for NLS pellets (I believe they're the only importer for the brand within the UK/EU), which are impossible to find where I live. Fast delivery and great customer service.
The Green Machine - http://www.thegreenmachineonline.com/
Possibly the best catalogue of high-end aquarium products (tanks, decorations, etc.) that I've ever seen online. Very interesting blog, too. They've got a massive plant selection here.