Best Quality RAM for 2009 iMac

I'm looking to max out the RAM on my late 2009 2.8 17 iMac. The machine originally came with 8 Gb from Apple. A few years back I added another 8GB of what was supposed to be Mac approved Crucial brand RAM that I purchased locally from Canada Computers. I had all 16 GB up and running, but the machine would freeze and sometimes reboot automatically during RAM intensive operations. I returned the Crucial RAM and was given another set of sticks to try (same brand & specs). Same issues came up again. I've pulled out the Crucial RAM and am only using the Apple supplied sticks (8GB). Machine is stable, but I get the odd beach balls due to low ram. Any suggestions on guaranteed RAM (and suppliers) that will work on my machine? I'd like to max it out again to squeeze some more life out of this iMac.

Thanks

via ehMac.ca http://www.ehmac.ca/showthread.php?t=111466&goto=newpost