Set up forwarding to one central account, and rules to label them. You can also set up rules about what the "FROM" address should be when replying. There have been rumors about multi-account support in Gmail for a while, but who knows if that ever will be made public, so for now the above seems your best option.
I have been using multi-accounts from Gmail for several weeks now. You need to go into preferences to enable it. Gives you multiple tabs/windows to see your e-mails.