For a long time I used yahoo. The nice thing with a directory is that if you found an interesting website you could look up similar websites in the same yahoo category. I think this functionality is just gone.
Are there any sites with a "crowdsourced" directory? Might be interesting to have something like wiki-pedia that is a curated source, but curated by a larger group of volunteers. Although, I could see it getting corrupted by marketing purposes, but at the same time it might be able to be maintained cheaply by a foundation. Human intelligence providing grouped sites might be a useful asset, and there could be statistics/requirements for getting listed.
There used to be dmoz.org, r.i.p. It doesn't seem to be working anymore, but it used to at least have an archive.