Directories have been good sources of one-way links for a long time.  It is 
a one of the easiest link building method especially for newer sites.  But q
uality is still the name of the game. Some pointers in selecting the directo
ries to submit to:

High PR - indication that Google sees some value in the directory.
Well maintained - listed sites are in the proper category
High Traffic - getting traffic could be minimal from directories, but majori
ty are targeted
Kewords ranking high in SERP - Well optimized, shows that the directory is w
ell-marketed and SEO'ed.

Which to avoid:
Link farms that pose as directories
Directories that require reciprocal links
Crappy ones with crappy sites listed

What are your thoughts?  Care to add more pointers?