After I obtained my first heart rate monitor, and GPS I obtained an android phone. With the GPS built in and lots of apps to go around, (plus being a developer I could, in theory, make my own apps) I immediately started wishing for a Bluetooth HRM, but didn't really have justification for the expense. Then I started learning about HRV, and thought that would be a great way to calibrate my training zone that I use with the HRM, but I needed a fancier HRM to do that. Looking around at fancy HRMs with integrated GPS, it seems that I'm a whole lot better off with my Android phone.
Here is my full listing of Android apps I found that support HRM (Compiled October 2012, I don't intend to keep updating it.)
If you are a developer, your best bet is Zephyr HxM™ BT Software Developer Kit. For $79 you get the hardware, and the developer's kit to get you well on your way to making your own software. You can also download the developer kit free separately from the hardware. While you're developing, there are several existing applications that can support your exercise or meditation needs, although I'm currently not aware of one that measures HRV.
If you're not a developer, you'll find many more applications available for Polar Wearlink®+ Transmitter With Bluetooth®. It retails at $79.95, and is a well respected HRM company. Beware though if you want to develop for it, I've only heard horror stories about contacting the company for an SDK. The MyTracks application supports it and is open source, so you should be able to pull implementation details out of there, but I'd rather support the company that supports open development. There is one app for it that I found that supports HRV.
There are a variety of little gizmos that plug into the audio jack of your android device that receive analog HRM data from your existing strap, but they generally only have one supporting application, and no SDK.
I'm planning on going for the Zephyr product myself...