What is the best form of marketing for an online directory?

[mohara_geminidawn]

I'm just in the middle of setting up a directory website for a specific target market in the marine industry but since meeting potential clients in person is not an option there seems to be a bit of a debate on the best way of getting people signed up. The options on the table are:
Via e-mail
Via mail shot with a SAE
or cold calling.
Which in your opinion would get the most response or is there any other ways you can think of?

[sugarhigh05]

Email, and maybe follow up with a phone call to see if they have any questions. Does it cost money to sign up? Maybe offer some kind of incentive if it does.

[Alex B]

I find that anyway you can give someone a sample before they have to buy anything, they're much more likely to buy from you. If you're looking to sell them something, find a way to give them a freebie that has value.

Then approach via phone first, and try to get emails. Your pitch will be for a freebie, so the chances of them turning you down will be next to zero, since there's very little risk for them.

[Phil Walmsley]

Word of mouth is always the best form of advertising that you can get.

[Angela]

Simple answer;
Micro social sites(twitter,friendfeed etc) = few weeks of work would give you 300-500 ppl to reach
Mailspam = %0.5 of click rate
Forum threats
GOOD SEO

[Julie]

Email, Yellowpages, social networking,