One of my current favorites in ANH...aboard the T4, when 3P0 finds R2, watch as R2 starts to roll forward (towards camera). If the shot had continued any longer, he would have just rolled straight into the bulkhead.
There's also some GUY in the Falcon's cokpit gangway behind Chewie as he's doing something in the cockpit...can't remember the exact shot though...
The shadows of Luke and Leia on the Deathstar can be seen during the "Didn't we just LEAVE this party" exchange between Han and Chewie, as L+L prepare to come running in.
How about the nonsensical conversation on Cloud City? As the heroes are walking with Lando, discussing the gas mining buisness, the conversation seems to have been pieced together...badly...from several versions and several takes...it makes no frigging sense.
Also in Empire, watch in the Asteroid cave, interior Falcon's cockpit. The "Captain, being held..." bit to be precise. Ford is mouthing the words along with Fisher, who aparently was so damn stoned most of the time, she couldn't get her lines straight.