A nice, simple sans that comes to mind with nicely unambiguous hybrid numerals* is Apex New – maybe worth a look. (I haven't used it myself though, so can't offer a first-hand opinion.)
http://vllg.com/Thirstype/ApexNew/mudTyper+Weights/

* I assume these are what you mean by «near-oldstyle» – numerals that diverge vertically, but only by a bit; their «x-height» is markedly larger than that of oldstyle numerals.

Thanks for the suggestion, but like most sans, Apex doesn't meet one of my most important criteria: bars on the capital I.

I found a few more likely candidates: FF Tisa and FF Parango. (The latter's numerals are a little wispy for signage & labels, but attractive for other uses.)

I'm a fan of FF Unit when unambiguous letter forms are required. It doesn't have a slashed zero though.

Another space-saving option could be Axel, with a slashed zero but no Italic styles.

Advertising disclaimer: I work at FontShop, but I have licensed both font families also for my own stuff ;)

Nina, Apex's alphabetics kill it for this task. The lc "el" in Tisa is too much like a numeral one. Parango has bigger problems... Unit is good - and the zero could be modified. Or you could use the o-slash. :-) Axel looks like a winner as-is.

Here's an idea: programming fonts! They're not the prettiest* but their glyphs are always highly differentiated. And there's a very handy one out there: Consolas! If you're on a Mac (or WinXP), Ascender sells it.

* And would the fact that they're fixed-width be an issue here?

hhp

Good points on Apex. I stand corrected. I didn't actually look at the alphabetics too much – kinda got hooked on the idea of hybrid numerals.

How about something in the general direction of OCR fonts, BTW? Even less pretty than programming fonts, but the glyphs are certainly just about as differentiated as they can be.

Good idea!

hhp

Consolas I have, and it's certainly a possibility (and monospace is OK), though there are some things I don't like about it. Programming fonts have indeed been used by libraries for call number labeling. When I make simple things in Word, however, the Consolas alternate OS figures don't appear in the character map; why is that? Does XP not fully utilize the Vista fonts?

OCR fonts tend to look a little bizarre, and are probably trumped by other options. Lowercase is almost irrelevant to my purpose, so Tisa is still a good choice. Thanks for Axel, which is new to me.

When I make simple things in Word, however, the Consolas alternate OS figures don’t appear in the character map; why is that?

I think that would be because the OS figures are included as OpenType features and not as separate characters. You would need a OpenType-savvy program for this. Choosing OS figures is possible in MS Word 2010 Beta (which you can try out free for now), but I don't think older versions of Word include these or many other typographically useful OpenType features.