So, you've decided you're going to host a Webinar. Now what? Other than posting it on WebinarListings (obviously!) there are a number of other ways you can promote your Webinar to get the word out, and here are a few:
Set up a Facebook event for your Webinar. While this may be duplicating the invitation you've created in other places (Eventbrite, GoToWebinar, LinkedIn, etc.), the viral nature of Facebook will help you in the end. When someone replies "yes", their Facebook friends will see that, and now they are aware of your Webinar.
Update your personal profile status and your fan page status announcing the Webinar, and a few more times before the date of the Webinar.
Facebook ads are also a great way to get the word out. You can be quite targeted, right down to the job title or location, and are reasonably priced. A typical pay-per-click (PPC) ad is around $0.60/click, but it obviously depends on how targeted your ad it. You will not only be able to see how many people clicked through to your event, but how many people RSVP'd because of the ad.
Tweet as much as you can about the Webinar the couple of weeks leading up to the date, without being overbearing. 
Most people don't start to think about attending a Webinar until a couple of weeks before, so you're better off waiting until then for your heavy promotion time. Be sure to ask people who are in your industry, or who know people who would be interested in your Webinar, to retweet it for you. Use the hashtag #Webinar, so if people follow that hashtag, they'll see it. And, I'm always happy to retweet good Webinars, so send me an @reply to @WebinarListings, and I'll RT it.
LinkedIn
Similar to Facebook, you can also set up an event on LinkedIn. Again, the benefit is that when people RSVP, the fact that they have RSVP'd will appear in the weekly emails people receive from LinkedIn about their connections' 
activities. This helps spread the word. And, utilize your status update in LinkedIn to promote the Webinar as well.
Many people don't know that you can advertise on LinkedIn. It's similar to Facebook in that you can select PPC or CPM (cost per impression), and target the ad appropriately. The ads are much more expensive though... the ones I've done have been in the range of $2/click.
Industry Publications
Depending on what industry you're in, there are most likely some publications that you can list your Webinar in for a fee. For example, for marketing, MediaPost and Read Write Web (RWW) are two good publications where you can advertise. Usually there will be a fee for these, and oftentimes it's high (i.e. RWW is $500/email), but the distribution will be high, and it will be targeted.
This post is getting long, so I'll cover the rest in the next post, including CraigsList, event invitations, mailing lists, videos, etc.! Any other ideas you want me to cover? Leave them in the comments below, and I'll add them for next time.
UPDATE: Here's part 2
