Just to clarify, because I think you might be confused - you might be mixing up earbuds (like those crap white ones that come with the iPod) with in-ear canalphones.

If you can wear a pair of foam earplugs, you can wear the Shure E1/2/3/4/5 series (yes, there is an E4 coming soon) or the Etymonic ER4/6.

My ear canals are actually two different sizes, even, and I can wear the E3 quite comfortably. A large tip for the right ear, a medium for the left. Like ScottC said, there are plenty of tip options:

For the e2: foam sleeves in S/M/L (like earplug material), rubber tips in S/M/L. They may now have the silicone comfort tips now also.

For all the others: one-size foam sleeves, rubber tips in s/m/l, silicone "comfort tips" in s/m/l, and the tri-flange silicone tips one-size.

I've never known anyone who didn't fit any of those tips. Whether they're comfortable or not for extended wear is another question, though - buy from somewhere with a friendly return policy, or make friends with someone over at http://head-fi.org who'll loan out a set