Get notified when you are cited! Sign-up for emails or RSS feeds from Web of Science
At this time, Web of Science is the big name in citation alerts (of the databases CUL subscribes to). Some publishers are now offering similar services, for citations in their own journals. For example Elsevier will alert you when you've been cited in any Elsevier journal.
Keep an eye out for this- more publishers will probably be offering this service in the future.
Create an alert for an individual paper:
Create an alert for a cited reference search (multiple papers)