Attached please find some potential logos. There are two general approaches: one sort of implies a unifying approach around a central "Lucene" theme, and the other is a standalone sort. And now, since LCF has become ACF, and ACF has become ManifoldCF, we need a whole new set.
"Lucene" themed logos
Classic with pictogram:
Standalone logos
These would be corresponding Lucene/LCF logos:
Here's another central-themed LCF logo, based around a bridge:
Another modest option:
New Apache-themed logos
(There are two other .svg files attached, but I don't have .png's for them yet.)
New ManifoldCF logo
Same logo with the TM, as required by Apache
The C and F make up a socket. The Apache feather make up the cord 
9 Comments
Mark Miller
So my preference would be something a little more understated - like the lcf "modest option" I posted above - but more polished and done in a vector format.
Karl Wright
Is there any particular reason for vector format over jpg?
Avi Rappoport
Vector is a zillion times more scalable than bitmap, so looks good at all sizes.
Anonymous
Apache prefers vector logos. They actually have some guidelines for logos (though I don't think everyone completely follows them).
Check out the solr logo contest page for some of the guidelines that Hoss dug up for that contest: http://wiki.apache.org/solr/LogoContest#Look_and_Feel_Guidelines
Mark Miller
That reply was me by the way - didnt realize i wasnt logged in.
Karl Wright
Should we run an official contest? Or just adopt the standards?
Anonymous
+1 for the more modest option. I had a plug or two "jacks" (I guess one male and one female) in mind. The big logos are not solid/bold enough for a logo, I think, and may have too many colours. I like the LCF emphasis in the modest variant.
Jan Høydahl
I browsed iStockPhoto a bit - here is some more logo inspiration: http://www.istockphoto.com/file_search.php?action=file&lightboxID=7663211&removeCache=1
Nicolas Max
Hello, During a break, I make this logo. Maybe too simple.