My parents had a few different reward systems they used at different times.
The first was just cash! Mom wrote out each chore on a colored index card. Yellow cards earned 10 cents, blue cards earned a quarter, green cards earned 50 cents, and pink cards earned a dollar. Yellow cards were things like "clean the light switches", "pick up and put away all your toys in the living room", "set the table for dinner", etc. We each had a section in the file box, and when we completed a task we moved the index card into our section. At the end of the week, she added up what we'd earned and that was our allowance for the week. Only did two yellow chores? You only got 20 cents. Did 10 pink cards? you got $10.
Another was "privilege points". We earned points towards privileges by doing chores, being obedient, etc. Watching TV, having a sleep over, picking the menu for dinner, etc. all had to be "bought" with privilege points.
Sometimes we had special deals worked out. I really wanted a stereo system, so my parents told me I had to earn it and show them that I could handle it. The deal was that I had to keep my room clean for a year, and then I'd get a stereo. If it got messy, they would give me a 10 day warning. If I failed to get the room cleaned up in those 10 days, I'd have to start all over again. It worked for me - it took me about 20 months to earn it, but I was thrilled when I did. 20 years later, I still have that stereo system!