I just use MS Word or MS Excel. I got the idea from all the RSL inventories I did as an Ordie. When I get home from a range trip, I just annote the differences, record the date, print it out and store it with the ammo. I use a digital camera for the pictures. Once I get a good pic, I use JASC's Printshop pro, (Most folks use Adobe's Photoshop,) to scale down and crop the pic so it fits in the document.
The hardest part about the pictures is getting good ones without a tripod. Natural sunlight is the best, but the neighbors might not be to understanding about me posing my guns in the lawn.
That and some of those old BP rifles don't even have SerNos.