Windows: CyberGhost VPN is a free utility that encrypts, anonymisesand offshores your internet use when you're using public Wi-Fi at an airport or coffee shop, or you're worried someone on your network is running a tool like Firesheep to gather credentials.
The service is built for users who just want secure, private access when connected from public or untrusted networks. The app gives you an offshore IP address and connects you to an anonymising server to mask your real IP address and location, and then encrypts all of the internet traffic between you and the VPN service. It may sound like overkill, but if you use public Wi-Fi networks on a regular basis, using a VPN is the best way to protect yourself from applications or web sites that transmit sensitive information like usernames and passwords in clear text.
CyberGhost VPN comes in a free version that will boot you offline after six hours or 1GB of data downloaded (although you can just reconnect when you're disconnected) or a premium version that ranges from 4 EUR to 10 EUR per month depending on how much data you want to transmit. The free version is likely to be enough for most occasional users.
CyberGhost VPN is an alternative to Hotspot Shield, which while functional, is known to disconnect randomly and experience intermittent connectivity issues. CyberGhost keeps its status page up to date, so if you experience issues, you can always check to see if there's a problem. Additionally, keep in mind that when using CyberGhost VPN, your connection is anonymised and offshored, so some location-restricted services may not be available. The CyberGhost VPN client supports Windows XP, Vista and 7.