Don't laugh, I'm serious. I am in the process of selling a bunch of brass and I need to do a lot of counting. Here is my process, which is much quicker and more accurate than counting out individual brass 1, 2, 3, 4, ..., especially if someone distracts you in the middle of counting.

Dump the brass out in a pile so you can get at it with both hands. Get a small box that will hold about 100 cases. This is so you won't have to re-do too much work if you suspect you have made a mistake. Repeatedly grab 3 pieces of brass with each hand and toss them into your box, counting in your head 6, 12, 18, 24, and 1 makes 25. I usually set the 25th case aside so I can get a rapid running total so far. When you have 100 cases in your box, empty it into a bag or whatever you will be storing the brass in and start over.

Kevin