I can't say for uppercase A, but I feel that the nicest looking sans-serif lowercase o I've seen was Charlotte San's. Admittedly, my experience is limited so I'm sure there's better out there.

Maybe /A/ from a very bold weight of Univers? Though it might only seem beautiful for being clever, and only seem clever in conjunction with the other characters, as intended. This might be a problem with your concept because seeing the characters in context is very important.

What about /A/ from Bell Centennial? Beautiful under the microscope, like an insect.

Beauty… difficult to define. Fascinating, like Meta's g, perhaps easier to find, but then you might end up with an alphabet of quirky characters only.

I am fascinated by sans serif /a/, it very easily looks jilted, pregnant, distended or over-biting.

The 'a' and 'r' of Univers 45 are exquisite.
The entire set of majuscules of DIN and Futura are as solid and well-constructed as they come.
Neuzeit's 'J,' Museo's 'U', Brandon Grotesque's 'g,' Akzidenz Grostesk's 's' are lovely.

I never know what to make of Univers /a/.
The hot metal version in Frutiger - Typefaces is a totally different character (literally, different personality) to what is available digitally, IMHO.

Thank you very much for your helpful suggestions! I loved especially Bell Centennial. It's beautiful! I think I am actually looking for these "weird" and special caracters as Meta's "g", 'cause I wanna honour outraging type-treatment and each character will get his own page, so no interactions and crazy combiantions. It will be like a postcard-collection (could be) kind of. So please go ahead with your ideas!

Folio's "Q" is also quite unique.

Are you going to include numerals?

lowercase "a" on Chaparral, lowercase "a" on Meta, lowercase "e" on Bree, lowercase "g" on Sabon and ALL Scala

Uppercase B in Quaadrat.

I think Antique Olive http://cl.ly/4L7L and Legato Sans http://cl.ly/4LFs both have a very interesting lowercase o.

Touché Frode!

Oliver Reichenstein (@iA) and I (@kupfers) started a similar project on twitter end of last year. Every week we post and volley the, in our opinion, most beautiful letter of the alphabet, starting with A in the first week and accompanied by a philosophical definition of the letter by Oliver.
Here is the website with my finds. For the conversation follow us on twitter.
Alas, our favourite o will take some time still.

Apropos Quadraat: I wish I had the skills to draw serifs, because I have an idea for a B that echoes Quaadrat, only the other way around.

Frodé

So let's see a table that shows the candidates for each letter!

hhp

So, now it's official. I'm done with choosing. Here the list of 26 sans serif lower case characters:

a: Arum Sans
b: Platelet
c: Tarzana Narrow
d: Monox (any alternatives please?)
e: Bree
f: Mentone Bold
g: Meta (of course)
h: Haptic Pro
i: FF Quadraat Sans Mono
j: Cholla
k: Bell Centennial
l: Mosquito
m: Scala Sans
n: Formata Pro
o: Armada Condensed Black
p: Urbana
q: ITC Kabel
r: Berthold Akzidenz-Grotesk Extra Bold
s: Xctasy Sans Bold
t: Charlotte Sans Bold
u: Phoenica Std
v: Roslyn MN Medium
w: FF Quadraat Sans
x: Hiroshige Sans Black Regular
y: Klint LT Pro Bold
z: Fontana ND

Thanks again to all the helpfull answers. As you see, I used a lot of the suggested fonts (maybe not the suggested characters itself, but at least...) and I learned a lot about typography (awesome!). Comments about my desicions are very welcome and if someone might have a better option for the "d", let me know.

To kupfers: A very interesting and inspiring project! I added it right away to my bookmarks so I'll keep up to date.

d: Perpetua?

hhp

The search is for sans serif fonts, Hrant.

You can judge whether it's beautiful, but Maple from Process Type Foundry has a pretty interesting /d/.

Oh, sorry.

Then I nominate the "d" in Peignot, which I actually don't find beautiful externally, but I do see as supremely beautiful in its sober pragmatism (taking into account Cassandre's overall intent for the design).

hhp

"You don't want beautiful letters, but beautiful words"—Mario Feliciano

I certainly agree with that, and it crossed my mind to mention it here myself. However the beauty of individual glyphs is certainly a strong motivator in type design, even if one ends up taming (or outright dumping) an overly-attractive shape.

BTW, that expression is much older than Feliciano. And a much better way to say it is: "A typeface is a beautiful collection of letters, not a collection of beautiful letter."

And of beauty itself: that's not even the main point to begin with! :-)

hhp

Hrant, I do like the version you quote. —I think I read it in Tracy's Letters of Credit, but I can't find it there now. I do think, though, the way Feliciano once put it me adds some insight. The basic unit of reading is the word, not the letter, so that's the goal: to make words readable and with the intended aesthetic, whether that is elegant, friendly, scary, beautiful, comical, rustic or whatever.

But "beautiful" is a very poor way to express what we try to get words to do.

BTW, the basic unit of reading isn't the word, it's the bouma. :-)
Longer words are broken up into parts (somewhat unpredictably).

hhp

Kuniberta, can you post a picture of the 26 letters you chose?

To hrant:

I love your phrase "A typeface is a beautiful collection of letters, not a collection of beautiful letter."! It would be awesome to use it for my book. Can you give me it's origins? Who said it, ect.? Thx.

To Mugford:

I was thinking of posting the whole book online(probably on behance network), with the treatments (different printing and use of paper) I'm gonna apply to respresent the caracters sou you can see what I did finally :). Hope that's ok.

And to eliason:

Maple it is! Very interesting! Thx.

I think I heard it from Carter, but I'm pretty sure somebody else said it first. Sorry, I'm not too good with historical references. I live in the now. Or something.

hhp

In this form it seems attributable to Tracy:
http://www.wikipublisher.org/wiki/TipOfTheWeek/00010

Apparently Carter used a slightly different wording:
http://desktoppub.about.com/od/typography/a/Typography_Quotations.htm