I just don’t think of the 70s as a particularly funny time for movies. Now this may have something to do with my age, I’ll be 40 in a few weeks, so I didn’t get out much till the end of the decade, but I can think of lots of funny movies from the 40s, 50s, and 60s.
So it is me, or is it the 70s?
Well, everyone’s sense of humor is different, but when I saw the title of this thread, my first reaction was “Young Frankenstein”. Also “Blazing Saddles”.
“Animal House” was a big hit, though it’s not one of my favorites.
I’m sure someone will be along with others.
My top 3 would be Monty Python and the Holy Grail, Blazing Saddles and The In-Laws.
What’s Up Doc
The Twelve Chairs
The In-Laws
Since you had both Woody Allen and Mel Brooks in their prime, there are quite a few classics:
**Bananas
Play It Again, Sam
Sleeper
Love and Death ** (The funniest Woody Allen film)
Young Frankenstein
Blazing Saddles
There was also:
Monty Python and the Holy Grail
Monty Python’s Life of Brian
I still crack up every time I see Kentucky Fried Movie.
Leaving aside Woody Allen, Mel Brooks, and the Pythons, everything I think of is partly funny but colored with seriousness: Being There, Shampoo, Network, Harold & Maude, MASH, Breaking Away.*
There’s the probably quite dated sketch movies Kentucky Fried Movie and * Groove Tube* – I last saw those on a drive-in double bill in 1979 or thereabouts. And there’s always Pink Flamingos if you don’t mind coprophagia.
The Goodbye Girl? Foul Play? Eh.
I loved The Bad News Bears when I was a kid. Disney movies were really second-rate in the 70s as I recall. Herbie, all those Kurt Russell movies…
Another vote for Harold and Maude.
Airplane
Monty Python and the Holy Grail
The Jerk
The Pink Panther Movies came out mid-70s. The good ones anyway.
Based on my DVD collection:
Blazing Saddles
Young Frankenstein
The Apple Dumpling Gang
Silver Streak
Oh, God!
Smokey and the Bandit
Being There
The Jerk
9 to 5 I feel is vastly underrated. (The movie, not working those hours.)
Doh! 1980!
The Exorcist. That split pea soup slays me every time.
That’s true but it reflected the era of the late 60’s through the mid 70’s. Before that time from the 1920’s to the early 60’s, it was common for the Hollywood studios to release broad and silly comic vehicles featuring whatever comedy star they had under contract (e.g., Universal had Abbott & Costello and Paramount had Jerry Lewis). However, by the time the last vestiges of the studio system faded away, movies–like the culture around it–seemed to get a lot more serious and weighty.
Phantom of the Paradise seemed particularly funny to me…though from the box office, I was clearly in the minority.
And agreed with anything already mentioned that was done by Woody Allen. I still frequently quote “Love and Death”…and I don’t think I am jejune at all. I am one of the least june people out there. 
“Murder By Death” should be on this list.
Woody Allen has been mentioned, but “Annie Hall” has not (or I missed it).
That was the last comedy to get the Best Picture oscar.
And so should “The Cheap Detective”, only more so.