This is just the 1970s games. No returning champions for any of the nighttime versions of games listed here.
Hollywood Squares
Daytime - straddled, champion was crowned by winning best two out of three games
Nighttime - did not straddle, champion was crowned by winning most cash ($250 per game, $50 for every X and O in any unfinished games) and wins a car
The winner chose a celebrity and won a prize worth at least $5000; the most expensive prize was usually a car.
Also, I think the amount won per game went up from $250 to $300 at some point.
Name That Tune, Celebrity Sweepstakes, The $10,000/$20,000/$25,000 Pyramid - no significant changes other than cash/prize amounts (Celebrity Sweepstakes awarded a bonus prize for winning the game in the syndicated version)
Special rule for nighttime (Cullen-hosted) Pyramid: if they didn't have enough time to finish the second game (they had not introduced the "fastest time wins" tiebreakers yet), whoever was ahead got $2500, which was split if they were tied.
Name That Tune went through a number of changes in its weekly format.
At first, it was pretty much just like the daytime (NBC Dennis James) format, except that in the daytime version, the Golden Medley was 6 tunes for $2000, while in the nighttime version, it was 7 tunes for $15,000 in cash and prizes, although a lot of times, that included an $11,000 52-day Mediterranean cruise that the producers figured very few contestants would actually take (one did, and he missed a tournament because of it).
Later, each Golden Medley winner came back the following week and tried to answer a "mystery tune" (usually a song you have heard before, but didn't know had a title) for $100,000 ($10,000 a year for ten years). This lasted for two seasons, and in each season, the contestants who tried and failed to answer the mystery tune came back for a tournament to win $100,000 in cash and prizes.
In (I think) the fall of 1977, they changed the format again; the two contestants played the entire show, with the Golden Medley being a buzz-in round, and after six weeks, the winners came back for a tournament with a $100,000 prize.
Jeopardy - 1974-75 syndicated winners received a prize based on the amount won in the regular game
Early in the run, there was a bonus round; there was a board with 30 slips, and each one had a prize - most had cars or trips (usually to Rome), but two had halves of $25,000. Also, most of the contestants were winners from the daytime version, at least at first (I am not sure when, or even if, this changed), and the player who was first to run a category in a game won a prize (at first, a car, but when they changed what the winner won, it became a trip to London).
The Gong Show - top prize increased from $516.32 to $712.05
In the Gary Owens-hosted shows, it was $712.05, but when Chuck Barris took over, it because $716.32, presumably to make it easier for him to remember. Also, a lot of the contestants were from the daytime show; in fact, at least one daytime winner got gonged on the nighttime one.
Sale of the Century may have had some variations between the last few months of the NBC version and the syndicated version, but I'm not familiar enough with either one to know for sure.
On the nighttime version, the winners played a bonus round, where they selected a difficulty level ($50, $100, or $200) and were asked three questions; if they got all three correct, they won a trip, a fur coat, or a car, respectively.
Also:
Family Feud - Fast Money was played for $10,000; also, while the daytime games were still played to 200 at the time, the nighttime ones went from 200 to 300, and then to 400.