Apple Intermediate Codec, H.264, MPEG 4 (Certain flavors), Apple Animation Codec, Motion JPEG A, DV, HDV. If you have one of the Pro Apps (Final Cut Pro, Logic), then ProRes 422 will work as well. That is not a complete list, but its all I can think of right now.
AVI is a container, not a codec. Just like MOV is a container, not a codec. You are correct in thinking you need a codec that iMovie can handle. I am not familiar with the converter you are using, but I would suggest picking one of the codecs I mentioned and put it in an MOV container.