The various websites turn these up (excluding Continental and Copa with their impending departure), let me know if there are any errors or omissions.

Aeroflot - “All unredeemed miles will expire for Members who have not had flight eligible for accrual in the programme or co-branded bank cards activity in the past 3 calendar years (from 01.01.2009 2 calendar years).” http://eng.aeroflotbonus.ru/about.aspx?ob_no=244#4

Aeromexico - “When do Kilometers accrued in the Club Premier Account expire? Kilometers accrued in the Club Premier Account never expire; you just have to fly on an AM code flight at the full public fare price once every 24 months.” http://www.aeromexico.com/usa/englis...les.html#4_FAQ

Air France-KLM (also Air Europa and Kenya Airways) - “Validity of Award Miles - As a Flying Blue member, you can maintain your Award Miles for life, simply by taking one flight* every 20 months on AIR FRANCE, KLM, Air Europa, Kenya Airways or Aircalin, or on any SkyTeam member. * Must be a Miles-earning fare flight” http://www.airfrance.us/X02/en/local...cekedgfndgij.0

Alitalia - “It is important to know that... The current edition of the MilleMiglia Program has a duration of three years, from 1 January 2008 until 31 December 2010, unless otherwise extended. If, after a period of 24 months, you have not completed a miles-eligible transaction with either Alitalia or other commercial Partners, Alitalia reserves the right to close the account and void any accumulated miles.
Qualifying miles are those that allow you to gain access or renew your membership in the exclusive Clubs. You can earn them between 1 January and 31 December by flying with Alitalia, Air One or SkyTeam Partner and Associate airlines and with other Partners, when specifically indicated.” http://www.alitalia.com/US_EN/millem...lemiglia08.htm

China Southern - “Sky Pearl Club mileage is valid for two calendar years. If your total mileage does not reach 20,000Km after two calendar years, the mileage accumulated in the first calendar year will be reduced by half.” http://skypearl.csair.com/Templates/en.doc

Czech Airlines - “Is it possible that my unused miles will expire after a while? No, provided that at least one active transaction (earning miles) is noted in your account in 24 months. If this condition is not met, all miles automatically expire in the account and cannot be used.” http://usa.czechairlines.com/en/port..._questions.htm

Delta - “Currently, miles will not expire as long as you participate in one of the following activities at least once every two years:
* Earn miles for travel on a qualifying Delta, Delta ShuttleŽ, SkyTeam, or other SkyMiles airline partner flights.
* Earn or redeem miles with one of the SkyMiles program partners including hotels, car rentals, Delta SkyMiles Credit Card from American Express, international credit card partners, SkyMiles Dining & Hotels by Rewards NetworkSM, MilePoint.com, mortgage lenders, CAP magazine subscriptions, real estate, or telecommunications partners.
* Buy Miles here at delta.com or by calling the number on the back of your SkyMiles card.
* Redeem miles on Delta, Delta Shuttle, a SkyTeam partner, or another SkyMiles airline partner.” https://www.delta.com/skymiles/about...ules/index.jsp

Korean Air - “Mileage earned in Korean Air’s SKYPASS program on or after July 1, 2008 has a validity of five years and any unredeemed mileage will expire. Mileage earned on or before June 30, 2008 will not expire. The five-year validity is calculated from the date of travel on Korean Air and partner airlines.” http://www.koreanair.com/