The Color of Truth - August 8, 1955 - S1-E7
Visible crew/equipment: The shadow of the camera is visible on the car's hood when Al is trying to convince Mrs. Melanie not to go after Sam. It lingers there for a while in the shot.
Thou Shalt Not... - February 2, 1974 - S2-E7
Visible crew/equipment: When Sam and Shirley go out of the bake sale to talk and she admits to having an affair and begins to cry, Sam reaches into his coat for a handkerchief, and a mic briefly drops down and is visible in the upper left of the screen. (00:29:00)
Another Mother - September 30, 1981 - S2-E13
Visible crew/equipment: After going to get pizza, Sam and the kids return home. As they pull in the driveway a long boom mike is visible in the back car window.
Leaping in Without a Net - November 18, 1958 - S2-E19
Visible crew/equipment: When driving to Denver we see the trucks with trailers go around a curve, and two modern cars are briefly visible on the right along with the knee of a crew member. The cars are probably the parked cars of the camera crew. (00:36:25)
Memphis Melody - July 3, 1954 - S5-E21
Visible crew/equipment: While Sam and Sue Anne are singing Amazing Grace at the diner, right after the shot of the cook starting to play the harmonica, in the next wideshot the actor's T-mark becomes visible on the floor at the bottom, left side of the screen.
Mirror Image - August 8, 1953 - S5-E22
Visible crew/equipment: After Sam tells Al the bartender that he wants to talk philosophy, Al tells Sam that he's not just the bartender, he's also the owner, then when Al walks behind the counter the actor's T-mark can be seen on the floor. (00:26:50)
Chosen answer: Per the Quantum leap page at http://www.scifi.com/quantum/episodes/season5.html. 8 August 1953: An enigmatic leap lands Sam in a Pennsylvania tavern, as his own grown self on the day of his birth. As Al and Gushie work frantically to locate him, Sam befriends a wise bartender (popular character actor McGill, who'd appeared in a different role in the very first "leap") and a group of coal miners. As a host of familiar-looking faces pass through the bar - with different identities than Sam remembers - Sam ponders his life of leaping with Al the bartender, who tells Sam he controls his own destiny. Pressed for more, Al the bartender simply shrugs and says, "Sometimes, 'that's the way it is' is the best explanation." Sam realizes he must right at least one more wrong before he can go home, and leaps back to tell Al Calvavicci's wife Beth (from "M.I.A.") to wait for Al, who will survive Vietnam and come home to her. The closing title cards state that Beth and Al have four daughters and will shortly celebrate their 39th wedding anniversary ... and that Sam Beckett never returned home.
Boobra