I actually just write down the figures I have, numbered, under the title of the line they came from. Whenever I get new figures, I just add to the list. May not be as efficient as a spreadsheet, though.
HOWEVER, if you go to REBELSCUM.COM, they feature something called "WEDGE ENGINE." There, they require to simply make a username and password, and you can go through lists of hundreds of action figures and collectibles, and add them to either your loose or carded collection. You can also grade the packaging if they're still carded. Also, the feature will make a complete list of the figures you have recorded, and will give you an average price for how much each item is worth. At the bottom of the list, it will tell you how much your overall collection is worth.