Dharmesh has some great tips, but he is too humble to promote his company HubSpot. The information he touched on about inbound marketing can be found in more detail at blog.hubspot.com. It is the definitive resource for online B2B marketing.
Also, buy Dharmesh's new book "Inbound Marketing" co-written with HubSpot CEO Brian Halligan. It's due out soon, but I am almost finished reading an early copy of it. It's a great book that really spells out the inbound marketing plan you should implement for your company.
Sorry to make this post so promotional, but I really believe in inbound marketing and HubSpot's methodologies. They have worked for my clients and for HubSpot's 1600+ customers.
Just remember this - companies are made of people. People that read blogs and participate in social media work at companies. Once you find your target audience and produce great content for them, you're on to a great start.
Now I'll speak directly to your needs:
Since the product is to be sold to
real estate developers, entrepreneurs,
investors and management companies,
rather then the tenants themselves
(since its for high-rise buildings),
then getting hype in twitter seems
pointless. As a start-up, we have
limited resources for marketing, so
sending agents across the country is
not an option.
Find blogs, news sites, and forums that these type of people might frequent. Make yourself known on there, provide advice, ask questions, and try to understand your target audience. Join relevant groups on LinkedIn. You might actually learn some things about your niche that will help you market better to them. Once you have a good feel for your audience, you can start writing good content on your blog and promote it on all the sites where you are a member and people know/trust you. This takes time and effort, but it works. Another book I would recommend about this is Chris Brogan's "Trust Agents".