I don't remember any of these shorts well enough to rate them, but I'd certainly like to see them again someday. Then I'd add ratings, and maybe expand my reviews a bit.
See also Cracking Contraptions and The Curse of the Were-Rabbit.

A Grand Day Out (24 minutes)
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The first Wallace & Gromit short film, from 1989. Everybody likes Wallace & Gromit, right? Well, you should. They're funny. Anyway, Wallace is sort of an amateur inventor. Makes some very clever contraptions, though he's pretty absent-minded. And he's got a clever dog named Gromit who helps him. In this story, Wallace realizes they have no cheese in the house- and he really likes cheese. So, he and Gromit build a rocket to go to the moon, since everyone knows the moon is made of cheese. (What most people don't know is that you can walk around up there without a space suit.) And um, there's some sort of robot up there. I don't know what else to say about the film, but I liked it.

The Wrong Trousers (30 minutes)
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The second short, from 1993. On Gromit's birthday, Wallace gives him a pair of "techno trousers" which can walk by remote control or whatever... Then Wallace decides to rent out a room to pay off some debts, and it gets rented by a penguin, who appropriates the trousers to pull a diamond heist. And that's about all I can think to say, but of course it's all funny and stuff.

A Close Shave (30 minutes)
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The third short, from 1995. This time, Wallace & Gromit get called to do a job washing windows, and Wallace meets this woman whose father was an inventor. And the woman has a dog. And there's big news about sheep rustlers. And um, I dunno what to say without giving away too much of the plot. But it's good.