Aside from the classic "city" mac fonts by Susan Kare, I'd say Mini 7 by Joe Gillespie and Silkscreen by Michael Kottke are considered tried and true by many.

What about Verdana? It seems to be about as ubiquitous as Helvetica these days.

Also, the designer of Silkscreen is named Jason Kottke, not Michael.
http://www.kottke.org/about

there's a movement in the last few weeks indicating Stan, which can be downloaded from www.miniml.com , is on its way to be a popular classic.

try oakland from Emigre - 4 weights and widths - very cool pixel font!

Hey, how about Geneva 12 px? It

This is a TheFoundry Architype Stedelijk!!!

(Stedelijk appeared on one of Crouwel's seminal posters of the period for the Stedelijk Museum in Amsterdam)

http://www.on-idle.com/freda/foundry_architype_3/images/text_examples/Text-ArchitypeThree3.gif

The first 'pixel font'???

The first pixel fonts were those on kilims (thin carpets), many hundreds of years ago.
Although I guess those were actually "lettering".

hhp

There's also mosaic-lettering...

And cross stitching...

Speaking on "first pixel fonts, I own two embroidery books, containing more of 200 full square flavored alphabets, most of them are very "enlightened" with more of 30 pixels x-height, but the small sizes, 7, 9, 10, 12, are very similar to our contemporanean screen fonts (Silkscreen and others)
They all came from the "Sajou", "Rouyer" and "Alexandre" embroidery booklets, from 1940/50 I think.

By the way, my favorite classic pixel font is Georgia in small sizes.

But if you want something that has U&lc, and suitable for body text and not just for navigation or captions, check out MiniHaha, the sister (or descendent?) of Mini 7. We're using that on our home page right now. The two faces work brilliantly together. Well worth the equally mini price tag.

Don't forget Sevenet, a free one from Fountain.
It's a good variation on Mini 7 and includes regular,
serif and unicase styles.

This one includes vector outlines that emulate the
bitmap (i.e. it's Flash compatible).

Speaking of the "oldest pixel fonts", if cross stitch alphabet specimens are allowed, these are among the oldest ones, ever: http://typophile.com/node/57604
Published around 1533.

(And yes, I know this thread is basically mummified! I figured that's befitting.)