I'm not sure whether you're looking for inventory management or accounting. I tried Working ARtist, found it too cumbersome and way more than what I needed. I then went to a spreadsheet on my computer and that was fine but I wanted a list that was available all the time and didn't want to have to print my spreadsheet every time I added something. Finally, I adopted the simplest system of all. For each painting, I make an index card where I record all the details of the painting, where I have shown it, what shows I have entered it in and who sold to. My little box has different sections for 'paintings for sale' and 'sold paintings'. I also keep track of shows and what I've entered in each that way, with an index card for each show. Simple but it really works and is always quickly available.
For accounting, you could try Simply Accounting. It's a nice and simple little accounting program. Although, being an accountant myself, I don't use it for myself. Again, the simplest route. I keep all my sales listed in my 'sales' book. I keep all my receipts in an envelope. At the end of the year, I tally everything up and prepare my profit and loss statement (more loss and profit I must say). For me this is simple as I used to do this for clients all the time, so I still find this the simplest way to do it for myself.