Charles Edge has an article posted about testing memory on Apple computers from the command line. If you have wanted to run a quick and easy memtest without booting to diagnostic media, then this is the answer you have been looking for.
Nate Walck
Nate is a Systems Reliability Engineer at Dropbox, Inc in San Francisco, CA. He runs afp548.com along with Sam Keeley and is one of the founding members of the ##osx-server IRC channel on freenode.net. He loves being involved in the Mac Admin community and using Open Source projects whenever possible, especially Munki, The Luggage and Puppet.
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Link is down.
Correct link: http://www.krypted.com/?tag=memtest
Thanks for the heads up. I fixed the link.