This is one of my favorite new business questions to answer and am planning on doing a full series of blog posts on building a brand and community. And obviously, I have a bit of work to do myself for this Q&A site, but wanted to make sure all the kinks are worked out before I go commando and push this whenbusiness.com to the bones.

Start thinking about your brand in a niche saturation context and what value your content/conversation can bring to the niche.

Obviously you've already started attacking some of the larger social networks, which is a great first step, but now you need to take a step back and do a little market research finding who maintains the heartbeat of the conversation and influence in your niche.

1. Find the top 25-50 bloggers in the niche and engage in meaningful (important!) conversation. Have something intelligent to say in replying to their blog posts. Your intelligence is your key to driving traffic back to your site. Have you ever read an intelligent reply in a blog post and followed their name back to their website? This is exactly the type of behavior you're wanting to encourage. You may not get google juice from backlinks to your site because of "nofollow" attributes on most blogs, but you'll get something more important, a visitor. Being one of the first to respond to large blogs, like techcrunch.com for example is a meaningful thing, and free to do. Technorati.com actually just re-launched and has a top 100 blogs, and which you can use to find those blogs that belong to your niche.
2. Aside from the mega social networks, there are literally hundreds of other social networks and message boards that you can newbies like you can leverage and is easier to have a voice because there is much less noise. Sites like Ning.com, have hundreds of networks for every niche imaginable. This is a perfect place to join and again engaging in conversation, and make a little noise at first, and more noise later as you gain a noticeable persona on the network. These social networks and forums, are really the key in establishing your brand.
3. Creating a blog and/or podcast, gives you the opportunity to continue engaging your audience with what you've learned about the current social conversation in your niche. This also gives you a direct voice in casting your opinion for your audience and then becoming an influencing presence within the niche yourself. When doing a blog, you can reply to another blog's post and leverage automatic pingbacks or trackbacks on meaningful topics. This is also an important way to establish relationships because these authority bloggers will now know who you are. They will see what you've written about their blog post. And you'll be listed on their authority blog site, waiting for their readers to find your title of the blog post interesting. If doing a podcast, ensure to do or use a transcription service. This is an extremely important way of getting a lot of free content written and works tremendously well with search engines (SEO). Don't worry too much about that audience at first, doing a podcast is difficult, for me anyway. Getting the equipment and production level right, is a difficult process. Just start out small, and if you need guidance on podcasting, i have a ton of resources. Have unique and meaningful titles, have a look at CopyBlogger.com for a series of tips, tricks and trends on what is working for blog copy.
4. Now that you have blogging and/or a podcast, make sure that you try to use aggregation services for your best material, digg.com, alltop.com, reddit.com, 9rules.com, etc.
5. Find available directories to put your business online. Places like technorati.com allow you post content yourself back to your site. Techcrunch.com has Crunchbase.com which is a directory of startup businesses. Then do all of the typical other directory sites, DMOZ.org, etc.
6. USE Posterous.com, even if your blog is on another platform, posterous allows you to quickly and easily create a synergistic brand concept, where now you're influencing the conversation on a whole bunch of platforms. Just by emailing a Posterous account they support many other social tools and networks, Twitter.com, Youtube.com, Facebook.com, Vimeo.com, Flickr.com, WordPress.com and Blogger.com blogs and more. You post once, and you post everywhere, social saturation, social saturation, social saturation.

7. This last one is my personal favorite, help people and the favor will be returned tenfold. Create tutorials or how-to's on your niche's subject matter helping people out, and they'll realize that you are a valuable resource to them. Then google tutorial aggregation sites for your niche. There are like 30 prominent players..

   Gonna say it again, Social Media Market Saturation!!! Hrmm, wonder if i can coin that term. Get out there, it's all FREE and yours for the taking. Say that out loud! It's FREE marketing, and you'll be smarter at the end of it all to boot!

By the way, thanks for asking this question, my blog post is now almost done. :-)

Some really good information here, thanks Robert.

Just wanted to add, that Kevin Rose had a great talk last week about taking your site from 1 to a million users.

http://carsonified.com/blog/web-apps/9-ways-to-take-your-site-from-one-to-one-million-users/

See, i just noticed that carsonified, took a video, and just broke it down and is probably getting a gazillion hits. That might be another way to get some traffic. Take a highly publicized speech/talk and break it down.

Here's another great answer from another blog posted today. http://www.dumblittleman.com/2009/10/7-free-or-cheap-ways-to-effectively.html

As well as The Clue Train Manifesto, especially the business conversation chapter.