The first is a rangefinder that you put on your sight window. Its a sticker that you line up lines with the animals back and belly. I ordered one to try it out. It was 11 bucks with shipping.
http://www.deadonrangefinder.com/
The next is a device that allows you to shoot without fletching as long as you us a drop away rest. It looks interesting. I use a whisker buscuit though so I didnt order on of these.
www.starrflight.com
Check them out tell me what you think.