Pangrams

"The quick brown fox jumps over the lazy dog" is a 35-letter pangram (a phrase that uses all the letters of the alphabet) that has been used to test typewriters and computer keyboards because it is nicely coherent and short.

In Windows XP, an alternative message Jackdaws love my big sphinx of quartz. 123456890 is added.
Adapted from Wikipedia
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There also exist perfect pangrams, where every letter is used only once.

These are some without proper nouns, acronyms, or abbreviations:
Veldt jynx grimps waqf zho buck. (A grasslands wryneck Woodpecker climbs onto a male bovid on Muslim land held in trust. - created by Michael Jones)
Junky qoph-flags vext crwd zimb. (An Abyssinian fly playing a Celtic violin was annoyed by trashy flags on which were the Hebrew letter qoph.)
Cwm fjord bank glyphs vext quiz. (Carved symbols in a mountain hollow and on the bank of a fjord irritated an eccentric person.)
Squdgy fez, blank jimp crwth vox! (A short brimless felt hat barely blocks out the sound of a Celtic violin. - created by Claude Shannon)

Confused? Here are some with proper nouns, acronyms, or abbreviations that'll make it more readable:
PR flacks quiz gym: TV DJ box when?
NBC glad. Why? Fox TV jerks quiz PM.
Blowzy night-frumps vex'd Jack Q.
Glum Schwartzkopf vex'd by NJ IQ.

Err, maybe not. =]
Adapted from Wikipedia