When hitting a new niche I join directly related organizations, societies... the ones that give the best quality 'member links' and have promise of good value; not just an endless list of links. Down the road, my membership may provide a wide variety of other benefits, but my membership alone is often a super bargain for good quality, targeted, one-way links. A couple of lines of provided text to go with the link - some of these links are a steal. Love related topic/niche organizations. The sites have often been around forever, are often underutilized but well respected, and often happy to be offered some 'free' content down the road a bit. Gold mines.
Not really into directories personally. Have never given Yahoo a nickel and never felt that it hurt any.