Well, at this point, with wireless technology so new, you are pretty much at the mercy of the people around you. I would say that your best solution would therefore be to do your browsing "off" of your actual machine.
Perhaps the best solution, therefore, would be to do your surfing thru a proxy. More importantly a proxy with SSL capabilities. I believe that someone here has already mentioned squid, and I think that would be an excellent solution.
Something else to consider would be the anonymous web browsers out there. I think one is at anonymizer.com... I have not looked into these technologies much, but I believe that the idea is that you sign on for the service, and you are able to do all of your web browsing through there proxy server (which features encrypted communications) thereby eliminating the clear text passwords eminating from your machine (as I believe that they would actually be coming from the proxy server).
Hopefully one of these suggestions will prove acceptable.