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 quality is still the name of the game. Some pointers in selecting the directories 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 form directories, but majority are targeted
Kewords ranking high in SERP - Well optimized, shows that the directory is well-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?