Take it from an old computer engineer -- rmeader hit the nail on the head. SSL/TLS or IPSEC is the best bet, and the only way to get it consistently is to use a VPN service. You don't control whether the web server provides HTTPS or not, and not all do. Similarly, in public hot spots the wireless connections are open to everyone and everyone can see everyone else's data (with the right collection tools). The VPN enrypts all your data in transit to its VPN server, which relays it out to the Internet backbone where tampering and monitoring are highly unlikely. There is a slight performance penalty, but if you can live with the performance penalty of HTTPS links then you can live with the performance penalty of a VPN since they are about the same. Besides, it is a small price to pay to guard against identity theft.
Using a VPN service means you go over every local connection using a secure tunnel, even the open ones like at marinas, Starbucks, and Panera Bread. Anyone monitoring your data stream, be it with Wireshark or some other packet sniffing tool, will see your VPN server as its destination for all packets and will just see encrypted data (which looks like nonsense). The destination then sends its responses to your VPN service, which in turn relays it to you via the encrypted link, aka the VPN.
There are plenty of decent VPN services and they are not terribly expensive. Read this article
at Lifehacker.com to find out about a few. You can Google for more articles too, if you like. I don't advocate for any one over the others. Do your homework and decide which is best for you.
One thing I will recommend, though, is choosing the OpenVPN client. You run it on your computer to connect to the VPN server. It is free, fast, and efficient open source software that is very high quality and is available for multiple operating systems including multiple Windows flavors, Linux, and OS X. If you are running iOS or Android you'll have to choose something else.
Is a VPN bulletproof? Well, no -- nothing is. But breaking it is very, very difficult. It is far more secure than your Windows computer! The most common methods to get at data over a VPN are to implant keystroke loggers or spyware on your Windows system using social engineering. What you want to do is keep your system free of infection and use a VPN. You become such a difficult target that hackers will look elsewhere for lower hanging fruit.