What's a good site to build decks on?

For a while I've kept a text document for each deck I build (that I have to order cards for), I try separating by card type and organizing by mana cost but it would definitely be easier if I used a site made for this task.

It'd be great if it also:

• Supported other card games (Pokemon and Flesh and Blood)
• Could export a deck to a text list (Mostly for proxying (are we allowed to talk about proxies here?))