8. All of the "vote for my comic" sites.
All of these give you the opportunity to get more exposure by putting your comic onto their lists. Just register, input their button code onto your site, and hope people vote, or even do what many people do, give them some incentive to vote by offering up a new comic or sketch of some sort. Some people find this corny, but it works to some extent. If I really like a comic, I want more, and that's where this idea comes in. Here are all of the ones I know of: Webbed Comics; Top Web Comics; BuzzComix; The Webcomic List; and Online Comics. Try any and all of these to possibly increase your viewers.
Now, PAID advertising? Not much different than anything else, just the money part of it. Project Wonderful is the main source of advertising in the webcomic world. There other ways(Adsense comes to mind, but let's focus on PW. Personally I love it, because it's simple to use, with it's easy to navigate website and creation tools for making ads(you can create buttons, banners, squares, half banners, skyskrapers and Leaderboards). The best part is that you can have as many ads on your site as you want, it's up to you. I prefer to limit the amount of ads on my site though because the more you have, the less demand, and the prices drop. Less ads, more demand, more money. Basically it's like Ebay: A person comes to your site and sees you have an ad up for free. They "bid" on the space and put their ad up there. It's free until someone else comes and sees the space and it may say "your ad here for .02 a day!" Then they get the space. Then someone else comes by and bids more, and so on and so forth. The more people bid for the same space, the more the price goes up. Unless you have 10,000 or so views a day though, don't expect to quit your day job, because this isn't the best way to make a living. But if a few bucks a month helps with hosting costs or just as a way to pay for your monthly bag of Gummy Bears, then try it out. Plus you can bid on adspace on other sites, as many as you want, to get your ads for your comic out there. Try putting your ads on relevant sites, because you want people to click, right? Don't put an ad for your comic, "Bisexual Adventures in Moist N' Sweaty Land" on a site called "Christian Kid and Bible Dude". I seriously doubt that would help you get hits. I have fun with PW. I love winning the adspace, but don't get caught up in the moment and bid on more than you can chew, or in this case, pay for. I had that problem with Ebay once. Not pretty.
There are tons of ways to gain viewers and make your comic successful, but it all depends on your willingness to go that extra mile. You can go the other route and just make a great comic and let word of mouth spread slowly, but I like to try and get my comic out there with the methods I mentioned here. I haven't tried them all, but maybe you will. No matter what reason you're doing this for, the end result depends on you. Just remember to have fun with it, because we're all in it for at least one reason: we like webcomics!