I've personally printed Amplitude Wide at 5 pt. and found the results very satisfactory.

On your leading question: in general I believe that pushing leading below 20% in order to use a large text size is usually folly.

These usual suspects were specifically designed for such tasks:

Ad Sans (Humanist 970)
Bell Gothic
Bell Centennial
Corona (News 705)
Doric
Excelsior (News 702)
Imperial
Ionic
Maximus
Olympian
Sans No 1
ATF Spartan
Spartan Classified (Geometric 212
Textype (Century 731)

I'd like to add that I've used some of these faces at relatively large point sizes and the results are always very striking. The exaggerated features and awkward proportions give quite unexpected results.

Actually, I'd be interested in compiling a list of contemporary typefaces that perform equally well at very small point sizes. Anybody feel like joining in with the fun?

Vialog is still quite legible at 4pt. The Munich transit authority uses it for their pocket maps (and timetimes, too, I think). Also, the new Linotype catlog's index makes use of this small Vialog as well.

Gotham is super-legible small, and it is pretty new and useful.
Metron (another transit typeface) is another highly legible one.

Between the two, I would say Metron can go the smallest: it has good ink traps, a pretty large x-height, and the counters are ovoid, so it is also a better space saver than Gotham. The problem, however, is that it is nowhere to be found on the Storm Type site, except in the 'best-sellers' list, whereupon clicking the link brings you to a mostly blank page with no information. I got mine with the Storm Open Library CD. Anyone know where to find it?

Very small size is one of the reasons Stefan Hattenbach’s Stalemate is being considered for a magazine redesign I'm working on. See it at

http://www.macrhino.com/

Franklin Gothic
Avenir

Not to forget Frutiger's Vectora, also specifically designed for readability at small sizes.

I think Celeste Sans works quite well very small.

Don't forget Gerard Unger's Vesta .

Lucida Sans

(nevermind)

I just received Typotheque's booklet about the Fedra family and noticed that Fedra Sans is extremely well suited for use in small sizes.

http://www.typotheque.com/

How about ClearviewOne?
http://terminaldesign.com/retail_specimen.php?ID=1001&viewFam=1

AT&T has been using it quite a bit lately in both their ad work and corporate communications.

I've been using Avenir lately on a client's project, and found it was very legible even at 6pt. I've actually laid out a lot of copy at that size simply because the face ends up looking too large when at 10pt.

+
Ryan Ford

These are all good ideas and as always you have given me alot of fonts to think about...

Thanks for your time and I will look through all of the fonts mentioned - will get back to you about the final font I used...

Thanks again

Isaac

Don't forget Mike Abbink's Kievit! FontFont set it small for their 2004-2005 catalog and it worked very well. It's my new sans favorite as well :)

Gotham is super-legible small, and it is pretty new and useful.
Metron (another transit typeface) is another highly legible one.
Between the two, I would say Metron can go the smallest: it has good ink traps, a pretty large x-height, and the counters are ovoid, so it is also a better space saver than Gotham. The problem, however, is that it is nowhere to be found on the Storm Type site, except in the ‘best-sellers’ list, whereupon clicking the link brings you to a mostly blank page with no information. I got mine with the Storm Open Library CD. Anyone know where to find it?

I got it buying the collection. Zeppelin is another storm type that can go small or large.

Oh, Formata will go pretty small as well.