I developed an educational app in one day. Apple featured it right around Christmas. Best Christmas present ever. I made enough money in that one month to pay off all of my credit cards and student loans. I even paid cash for a late-model car that month. Part of that money also helped my company lease a kick ass office. We went from subleasing a dark attic above a video production studio to leasing our own class A office.
Wow, what was the app?
A long time ago I made some silly music visualizations for Winamp that ended up shipping with the official download. Years later, a picture surfaced showing an astronaut on the ISS using Winamp on his laptop... which means my code made it out into space.
Best reward ever.
I started an alternative medicine affiliate site back in the summer of 2006. Probably spent 4-5 months full-time on it, and 1 hour since. It made me $1.6 million total for the first 2 years before I sold it. Pretty good ROI.
I built a side project on a weekend and made $700 from revenue / selling the site. It also helped land me a job. Not too shabby.
Fired a big'n'awfull client once, gained months of happy living.