I've only been doing this for about 3 months, but in that time, we've racked up some pretty good deals. Some of these cards I've had for a year or longer.
AA Visa 75K miles
AA Visa (wife) 75K miles
AA Amex (wife) 75K miles
AA Biz 75K miles
Chase Sap Pref 50K points
Delta Reserve About 60K miles with my spend and miles boost
Delta Plat Biz About 50K miles with my spend and miles boost
Citi Thank You Had for like 10 years, no intentions to close, no bonus
Chase Ink Biz Just use it for Sams since they only take MC
SPG Personal 30K SPG points
SPG Pers (wife) 30K SPG points
SPG Biz 30K SPG points
SPG Biz (wife) 30K SPG points
Only Annual Fee cards I will keep is the Delta Plat Biz ($150), because the free companion certificate is worth more than that, and the Delta Reserve, because the MQM/miles boost, free Sky Club, and another free companion certificate is worth it.