http://en.wikipedia.org/wiki/IMAX#IMAX_3D
Wikipedia suggests that IMAX 3D uses either linear polarization or LCD shutter glasses. Obviously 2-D shutter glasses wouldn't be very practical, but the polarization glasses (which I think is the standard?) should be just as feasible as the circularly polarized glasses used by RealD.
Come to think of it, normal polarized sunglasses should work as linear polarization filters assuming they line up the right way.
Every pair of polarised glasses I've tried has been polarised at a 45 degree angle; this helps with more consistent glare reduction and also means that LCD screens don't appear completely black half the time.
I've actually marked the edge of the circular polariser filter I have for my camera so I can tilt my head (wearing polarised glasses) and then quickly move the filter to match.
I thought the the point of having polarized sunglasses was that they should be polarized vertically in order to block glare (which tends to be polarized horizontally; see http://en.wikipedia.org/wiki/Brewsters_angle). Mine are, anwyay. Usually it is the LCD screens that are polarized at a 45 degree angle - for compatibility with sunglasses.
I had Lens Crafters make me a custom pair of polarized sunglasses with the polarization at 45 degrees to match up with my laptop's polarizer. Used with the laptop, they dim everything I see BUT the laptops screen. Not all laptops have the same 45 degree tilt, some are 180 from mine.
Come to think of it, normal polarized sunglasses should work as linear polarization filters assuming they line up the right way.