In the capitalistic model, it's money. But we all know (hopefully we all know) that money isn't everything. So, then what does motivate us? I thought this video had an interesting answer:
I thought the results of higher financial incentives leading to worse performance in cognitive and creative jobs was telling. It mirrors my own experience. Don't get me wrong. I DO like getting paid and would have absolutely no complaints about earning more money. But that's never been the drive behind my choices. I was groomed for and pushed to medical school most of my youth, primarily because the medical professions pay well. That didn't sit well with me since I'm pretty sure I couldn't stand doing a job I hated merely for money. So, I became a black sheep in the family by going to engineering school. There are a ton of jobs out there that I could have done that would be paying a heck of a lot more than I earn now, but I decided that job misery simply wasn't worth it.
As a side note: if monetary incentives are mostly ineffective at boosting job performance, you have to wonder why it's so commonly used in the financial sector. That would seem to select for greedy, self-interested people who get dumbed down by the financial incentives. Maybe that's not the greatest combination for an industry which drives a large portion of the country's economy.