Here are some links to New Yorker cartoons in case you need inspiration or are wondering how the image and caption should play off of each other.
My favorites:
Tape Dispenser
I remember this one from when I was a kid
The Classics plus random ones found on Google Images that made me laugh:
On the Internet...
Snowy Sight Gag
Building Blocks
New Take on an Old Saying
Lifeguard
Cute Jewish Joke
Doctor Humor, Ventriloquist Humor
Two great funny tropes thrown together!
Cute Dog Joke
When the Cat's Away....
A few of the thousands of entries from the Cartoon Kit contest held in 2009, in which participants were invited to create their own talk-show situation from pre-drawn elements and give it a caption. They provide an excellent example of the variations that are possible with one simple, iconic theme:
Cartoon Kit entry #1 - Cartoon Kit entry #2 - Cartoon Kit entry #3 - Cartoon Kit entry #4 -
Cartoon Kit entry #5 - Cartoon Kit entry #6 - Cartoon Kit entry #7 - Cartoon Kit entry #8 -
#9 - this one took me a few moments to get. - Cartoon Kit entry #10 -