See here for upcoming deadlines for ACM Award Nominations. Most if not all of the nomination deadlines are November 30, 2016. As usual, the CATCS is available to help with the nomination process (in the form of providing advice, connecting you with others who might help, etc.); just contact a member of the committee.
Note that for ACM Fellow Nominations, the candidate must have been a Professional Member of ACM (not just SIGACT member) for at least 5 years continuously.
In addition to the awards listed at the site above, note that there are also several SIGACT-specific awards.