Previously mentioned Hotspot Shield VPN has been available for iOS for a while, but now Android users can take advantage of the service's free VPN service on their phones and tablets too. Once installed, you can fire up the free VPN to protect your email, web surfing and social network browsing from prying eyes on Wi-Fi or even on 3G.
There's less of a need to protect your browsing on 3G cellular than when you're using publc Wi-Fi, but Hotspot Shield offers protection on both. Basic encryption for all connected apps and browsers is included with the free version, but while Hotspot Shield is free, it's also ad-supported, so be aware of the trade off you're making to encrypt your traffic: you're protecting your passwords and data, but you have to trust Hotspot Shield with where you're browsing. You can eliminate the ads by signing up for a $US1.99/mo, $US19.99/yr "Elite" subscription, which also offers private browsing, malware protection and bandwidth compression so you don't hit your data caps.
The app is brand new and in beta, so expect some bugs here or there. When I tested it, it worked without issue on my Droid Bionic, but my rooted OG Droid complained that Wi-Fi encryption wasn't supported. We tested on a few other devices with mixed results too, so your mileage may vary while they work out the kinks. Hotspot Shield supports Android 2.0 and higher (but not Honeycomb or ICS yet) and is available now at Google Play.
Hotspot Shield VPN [Google Play]