we just started using a program called asset. the thing is massive and very cumbersome. it has an iphone app that allows the phone to be used in the field.
i hate it so far, but i figure i'm just using it wrong. i see the potential. when i eventually get it figured, it'll handle every step from proposal to billing, with inventory broken down per truck and what's in general stock (not that i keep much).
I gotta set aside a few days this week and dive into it and get it set up so it'll work right for me in the field.