A product or item that is endlessly upgraded or improved and which users don't mind having to pay full price for the latest examples. A frequent occurance within video games.
EA Games have two cashcows - "The Sims" and the "FIFA" series of games. Neither of which I'd play if you paid me.
bitch who's just after a blokes money
Damn, that bitch was a cashcow! she like spent all my cash, and then I saw her at a nightclub with one of my mates!