For my purpose, it should have 2 criteria:
1. Search engine robot should have no difficulty in crawling any pages/links on the directory. So it's either static html or have a mod_rewrite.
2. The links entries should be recognized by search engine as a link back to the site.
I've check your suggestions, and I think I'm going to use CPLinks, it seems very good.
phpMydirectory.com seems good to but I think it just too complex for my purpose.
As for PHOP Link Directory, I cannot find the link, but it's no problem, CPLinks just suit my need.