When I advise clients on
SEO, if they have the budget absolutely Yahoo! paid directory is on the list. The key is knowing how to write the submission - they, like DMOZ, will decline your submission AND keep your $200 [it used to be $300!]. DMOZ is crucial, but is of course free - again, the issue is knowing how to write the listing so it's accepted.
It it's at all gimicky, or sounds like an ad it's an automatic rejection. Check out other listings on DMOZ in your industry, or your client's industry, for samples of 'what works' and follow suit. Note that most listings are one sentence, not more. Link title is the
actual business name, not a keyword-stuff.
With all that said, I think SOME paid directories can be worth it. There are also a lot of free directories that, while you'll get a link back to your site, can do more harm than good. Avoid the really junky link farms, paid or otherwise - you'll know them when you see them.