USPTO PAIR Includes Patent Expirations
According to a post by Carl Oppedahl to the PAIR Listserv at www.patents.com:
The USPTO's PAIR system now lists patent expiries. Not all expiries, but those that are due to failure to pay maintenance fees.
For example, look up Patent Number 5,844,661 in http://portal.uspto.gov/external/portal/. It now has a status of "Patent Expired Due to Non-Payment of Maintenance Fees
Under 37 CFR 1.362."
It says the status date is January 2, 2003, but as recently as a month ago there was no mention in PAIR of the patent expiry for this patent.