rEFIt defaulting to 32bit kernel
At the OS X command line, try: sudo nvram boot-args="arch=x86_64".



EDIT:

Try resetting your NVRAM to get you back into OS X.  Since we added a value to the boot-args variable in NVRAM, resetting it will clear it out.

If/Once you get back into OS X, try the following per Apple:

sudo systemsetup -setkernelbootarchitecture x86_64


Rather than write into the NVRAM (which was likely modified by rEFIt), this writes a value to com.apple.Boot.plist and persists on the volume.