I'll agree wholeheartedly! There are so many opportunities available in the niche directory marketplace that are still untapped. Small highly targeted niche directories that get local and national advertising (if applicable), are an excellent business model. Particularly in today's market place where the global directory business model is failing or has failed.
I work with many local clients and the quality of visitors we receive from local resources far outweighs anything the major directories are bringing in most instances.
So, what are the top ten directories? Those that are bringing the quality visitors to your site. Everyone's list will be different and probably won't apply to your needs. The global directories are good for one thing these days, distribution amongst their feed partners, that's it. Oh, and maybe a little bit of PageRank. ;)