The two I like most are DiscoverIT and Costco Amex. I've earned ~$800 with the Discover card, and ~$400 with the Costco card. Additionally, you can link Amazon to the Discover card, so whenever I check out on Amazon, it shows my cash back balance and asks if I want to apply it to my order. It's nice to get the occasional freebie order.
Only downside is I still have to pull out the Visa card once in a rare while, as some places take neither of those.
I put all my expenditures on the cards - utilities, tax bills, cell phone bill, etc. The power company is one of the few that only takes Visa/MC. Both accounts are set to Auto Pay the full balance every month.
I spend ~$40k on Discover, and ~$10K on the Costco card. That's just about our entire budget, except for the mortgage.