Google ScholarSet up citation alerts to be sent to your email whenever an article cites your original source.
from the Google Scholar site: Google Scholar Citations provide a simple way for authors to keep track of citations to their articles. You can check who is citing your publications, graph citations over time, and compute several citation metrics. You can also make your profile public, so that it may appear in Google Scholar results when people search for your name, e.g., richard feynman.