I think, adbanners, text link, and announcements on high traffic sites. giving away free things, etc....
i'd say sitewide links / paid directory submission [let the people know you are in the biz] / sponsor some templates or just give something for free.... and you are there
www.directorycritic.com http://info.vilesilencer.com/ or to buy some text link on webmaster site. such as http://www.searchenginejournal.com/ if you got that budget..
I voted buy sitewides, but the answer depends on your budget. if you can't spend money, then forums and free submission will do it, slowly but right.
To get bulk submissions you need to be promoting and marketing on the net 365/24/7 there is no shortcut That means promoting everywhere you can because heavy traffic/and contacts are what you are looking for to provide you with bulk submissions
Question: Do you submit your directory into a highly respected directories (read: expensive) with high PR or just with normal directory?
i submit all over the spectrum..from pr0 to pr7 and 8 i feel the more links the better,if for anything, traffic..
You missed out the best way IMO, the best way to promote any site, three words "Search Engine Optimisation" my directory still has some trust issues with Google and Yahoo but very soon they will start loving it off, it already ranks very nicely on http://uk.msn.com shame no one uses it.
Hmm I wouldn't say it's the best way.. I agree it's quite a vital part.. but not the most important..
Hmm, it didnt even cross my mind really, I think your right though, maybe a new thread about dirctory SEO needs to be made.