You mean like Google? Search engines in general? if not, one site I always like to get a BURST of hits from is Stumbleupon. You submit there and youll see several hundred hits that day. Problem is, it only lasts a day. I do this after I make a new site or write a new article. It gets some nice traffic that often ends in a bunch of backlinks and gets the site/page indexed faster. Good Luck
It depends what market you are in...if you are going for the high traffic keyword, then everything. If you are promoting affiliate offers then basic article sites like ezinearticles.com, digg, mixx, and a few press release sites should do the job over time.
So Ezinearticles allow affiliate promotion? I mean of course it has to be good content, but linking to an affiliate is acceptable?
promoting affiliate links directly no, you can bring them to your website first, and have an affiliate link on your page, which is what you should be doing for SEO. Articles about the affiliate product usually have to be reviews and not sales pitches
I recommend submitting your site to Technorati. I did a few days ago and am already seeing an increase in traffic
I agree that StumbleUpon gives a nice little temporary traffic boost. I also like ezinearticles. If you're lucky, you get some love from Digg. Finally, I would go with delicious. I am testing our Fark now. Especially since they offer some tracking and you can see what articles are providing click-throughs. I've had similar success with Yahoo Answers.
Don't forget google local. If you structure your business name correctly you can get a lot of traffic. If you type "San Diego Hiking Trails" in google you will one of my sites ranks #1 with a map. This is a new site less than a month old that is getting an extra 40-60 hits a day.
I suggest Dmoz/ODP - you might be waiting a year or two (maybe even more) but its definitely worth it as the submission goes to Google's directory as well as others.