There are a TON of options. If you mean at the laptop / desktop end and not the router end, start with something like this http://www.amazon.com/s?ie=UTF8&field-keywords=alfa There's a whole market for people who live on sailboats and need to get wifi from the marina, and for wardrivers as well tbh. $30 and you're all set. On the router end consider an antenna upgrade e.g. http://www.amazon.com/Cisco-Linksys-High-Antenna-Connectors-HGA7T/dp/B0002F3G7M if there's something compatible with your router, and also consider a nice open source firmware upgrade which lets you jack up the router power such as https://en.wikipedia.org/wiki/Dd-wrt or https://en.wikipedia.org/wiki/Tomato_firmware .

If you are using a wifi modem that gets Internet service over a cellular plan, then you need to boost your cellular signal. You need to buy one of these, making sure that it uses the wireless signal band that your Internet Service Provider does. On the other hand, I bought one of these, and found that it works indifferently. Other than these, there is no real, good solution.