Anytime I go to a sensitive site (my bank, etc.) I make a habit of first attempting to login using a bad password - on purpose. If you somehow got spoofed or received a bum DNS reply, the bogus site will probably let you in with any password. That would be your clue that something has gone amiss. You have to have multiple layers of protection, topped off with the most important layer of all - your common sense and wariness.

If you're really wary, don't do any online banking or sensitive stuff like that, and do all your websurfing using a LiveCD like Knoppix (with all your harddrives unmounted). If you're really really wary, don't plug the network cable into your computer. If you're really really really wary, don't use a computer. No computer is 100% secure, unless it's also 100% non-functional.