There is a new service that I have been working on to allow those like myself that buy and sell Bitcoin to keep track of all of your transactions and averages easily and free. Basically the service will let you enter your transactions to find all of your totals and the average price you not only buy BTC for but also BTC sales and what you need to sell for to make a profit. This free service is called Bitcoin Cash Book (its like a ledger that gives you totals automatically).
You can currently register for a free beta account at Bitcoin Cash Book via http://www.bitcoincashbook.com‘s registration page. Open beta registrations have just started today. You will notice when you go to the registration page that the invite code is pre-filled. If for any reason the pre-fill does not show up for you the invite code is “14367”.
Keep in mind that this service is free and will only be available as is. Also the service is still in testing stages and will likely have bugs throughout. The account now will always be free and will remain active after actual full release of service.