I am using "Mini BMS" http://www.cleanpowerauto.com/MiniBMS.html
, The Centralized version. It is a little pricey but it works very well and it is shipped from somewhere in the US. They answered all my question very promptly.
my bike has a relatively large pack 100v x 16ah headway so I detach the bms while I ride and only use it to plug into when charging. The BMS will turn off the charger when hvc has been reached. I believe it has 1amp shunting capacity, (but don't quote me on this). I have been using this BMS with 2 48volt CC CV DC power supplies wired in series that I bought off ebay. it has been 6 months now and my cells are balanced within + - 0.01 v of each other.
When I say that I don't ride with the BMS attached that is not to say that I couldn't, it is just that I have a large bank and I monitor the overall voltage with a cycle analyst. My mileage around town isn't enough to bother with attaching the BMS. However for long trips I would defiantly attach it (as well as the charger) in which case my pack would be monitored and I can plug into any 120v outlet to power up. the BMS sounds an alarm when LVC is reached.
another nice thing about this unit is that it is expandable. In my case when I first built the bike I was running 72v but then I decided to up to 100v (since I just had the batteries sitting around), I only had to wire in a small shunt in the board to make it configured to 30s instead of 22s. The company also tells me that instead of a shunt I could wire in a simple toggle switch that could allow me to monitor between 22s and 30s (or any other configuration). This was something I was considering because the way the bike is built I could take off the extra 8s and use 22s when I take the train to different cities (with only 22s it will pass the weight requirements for bicycle for the train company (i.e max 72lb) otherwise I wouldn't be able to take the bike on the train.