Chrome: Comparison shopping is always kind of a pain, and it's even worse if you're trying to do something more complicated, like putting together a PC or an outfit. Agora is a Chrome extension that makes that process a little easier by giving you a place to organise your shopping where it's easy to compare everything.
With Agora, you just need to drag a product image down to your "belt", and Agora saves that for you. Once you grab a bunch of various products together, you can compare them all in the "workspace". This way, you get an easy way to look at several products from different retailers all in one place. Currently, Agora is in beta and only works for a handful of more popular shopping sites, but it's expanding as it goes.