Motorola Defy is the newest one to this. The device is $150 and comes with a year of free messaging. One of my buddies is getting one for our next trip. If it works out, I'll probably switch to it.
I use Zoleo and have for a couple years. I've been pleased with it so far. I did message their warranty department about my battery's life, and their response was that I needed a cord. I asked how a cord impacts the longevity of a fully charged battery, but apparently they didn't even know - some very complicated physics or wizardry at work! Their warranty dept is pretty awful, but the device is handy enough. I'll end up getting a new battery for it on Amazon - but, like I said, if that Defy works for my bud, I'll probably switch to that based on cost.