RJ,

The only one I have used, and you are probably used this one before is the ProChrono from Competition Electronics.

Here is the LAS link:

http://www.lancasterarchery.com/shop/product_info.php?cPath=46_213&products_id=2130 &osCsid=26bf330cf790cd28f04da8cdabef9c48

From what I have used it, it seems to be accurate. I am sure others might have more "vital" information about chronos and such.