Trainz Auctions offers a free online inventory program that ties into their database, so you get pictures, description and even auctioned value range. I like that you can download it to Excel so you always have a backup. I've bought stuff from them and you can automatically add those items to you inventory. It's functional for my needs. I hope that helps,
Unless they changed, I found Trainz Auctions limiting in that you can not sort your collection.