Go hurry, the rebates are scheduled to end on January 31st.
If you are planning to use the lens on a tripod, I can recommend the tripod collar from Fotodiox (check on Amazon) for around $40. The original Canon tripod collar for this lens is ridiculously expensive. But I haven't really used it on a tripod other than testing/playing around, so you might as well not buy a collar at all.