If it's just four letters, hand letter it.

The usual list: http://fontfeed.com/archives/helvetica-and-alternatives-to-helvetica/
And Akkurat at Lineto: http://www.lineto.com/
Dada Grostesque: http://www.optimo.ch/pages/departement/index.php?id_categorie=1&id_font=18
Galaxie Polaris: http://www.vllg.com/Village/GalaxiePolaris/mudTyper+Weights/
Kai Bernau's Neutral: http://www.letterlabor.de/
.et al

I love Akkurat. It has a sort of lo-fi "hipster" quality about it. Its use on wolffolins.com is a perfect example of that quality.

Getting a little further afield:

Whitney
Me
Ingrid
Underground

Thanks everyone. I must say I love trawling through this site when I have time and attempting to increase my limited typographic knowledge. The threads are almost always helpful, entertaining and interesting. Well done.

Akzidenz Grotesk or Folio. ;)

Sort of parallel to what Steve said: the ideal logo is not just a typeset font. You could just as well start with Helvomita Olde as long as you then take the canned result and craft it towards what the "iLab" string wants and most of all what the client needs (which is not the same as what the client says it wants).

hhp

Also have a look at Kris Sowersby’s National.