I've created a Hearthstone collection tracking spreadsheet. It is based off of a similar sheet I found on Reddit, only I cleaned it up a bit and made it easier to use and read.
https://docs.google.com/spreadsheets/d/1p94gq_GGTw8L1MeyBOCwoGu6nsjcGP8W_U9vsL8hTLQ/edit?usp=sharing
To use, just download it or make a copy into your own Google Docs account. Then start filling in all the cards you have, up to 2 for commons, rares, and epics and 1 for the legendaries. Once it's all filled in, the spreadsheet will give you some details on your collection including how complete it is, how much dust you would need to craft the missing cards, etc. For example, my current collection is 51.66% complete and I would need 87,040 dust to complete it. (Gulp.)
I'd like to add support for golden cards next. And then maybe the ability to add more than 2 copies of cards. Then you could get an accurate assessment of how much dust your current collection is worth.
Try it out and let me know if you find any inaccuracies. Thanks!