From 1996 through today, from the American Presidency Project. Let’s hope Obama doesn’t mirror President Clinton’s address that followed his 1994 electoral setbacks (the second-longest on record at a whopping 1:24:58; Clinton also owns the record for the longest — 2000’s swan song came in at 1:28:49).
Perhaps it is too much to hope that Obama will feel more comfortable in Jimmy Carter territory? Carter delivered the shortest SotU on record, just 0:32:04, in 1980.
UPDATE: CNN reports the president’s speech is coming in at about 70–75 minutes, with applause. But judging from what we know about all the Democratic infighting, maybe 60–65 minutes is a better guess.