Google Adsense is the easiest way IMO, until you get banned. I got banned while I was on vacation and I still have no idea why.... PPD sites seem to be the second best bet. A steady income with little to no upkeep after a few days of work is very achievable. It's best to put some money into marketing the sites. Or, you could just buy five litecoins and watch it go up 50 dollars a day..