So i finally got my dSLR. I was thinking of getting the canon 100 macro lens, but have also seen a lot of people using the sigma 105. Any thoughts or suggestions would be greatly appretiated. Thanks.

My recomendation would be the Canon 60mm macro. This focal length is much easier to use than more telephoto macros and is more appropriate for most macro subjects. Unless you love gobys and shrimp and dont care that much about larger fish (wrasses, parotfish, butterflyfish, angelfish, ect...) the 50-60 range is a better chioce. Remember that if the subject is more than 2-3 feet away, dont bother. That means with a 100mm lens anything bigger than about 6 inches is going to be to big to fit in the frame at that distance.

The canon 60 is a much more modern lens (better AF, Full time Manual Focus...) than the 50mm macros from canon and sigma.