From Zemanim.org comes a very useful site that - given a departure and arrival location, date and time - will calculate the amount of time after take-off until you reach significant halachic times like Sof Zman Kriat Shema, Tefilla, Sunrise, Sunset. (Here is an explanation of how these are calculated). Very useful for traveling to Israel.

April 27th, 2006 at 1:47
hi, I am flying out of Newark tomorrow at 2:30PM and arriving in Tel Aviv at 7:45AM Friday morning. I would appreciate if you could e-mail me the in flight z’manim. I am leaving to the airport tomorrow morning, so I hope to receive an e-mail before tomorrow. Thanx and tizku l’mitzvos.
April 27th, 2006 at 8:44
You can use this page to calculate what the Zemanim are for your flight.
September 27th, 2006 at 19:08
I’m leaving to Israel today on the 27th of Sep. at 7:55 PM. i would like to know the appropriate times for Shacharis,etc. Can you please get back to me as soon as possible. Thanking you in advance.
September 27th, 2006 at 21:30
Please consult the site linked above for your specific case.