I built a consulting company from 0 to 30+ employees in 4 years, so I got pretty good at this. A few ways that worked for us were (listed in no particular order):

1) Google Adwords to a free piece of content (ebook, webinar, etc)
2) Speaking at conferences, and being religious with "following up"
3) Leveraging our current customers for referrals early in our project (early is better then after)
4) Teaching our team how to identify opportunities when they were working with a customer to feed that to our account managers.
5) Blogging.
6) Create simple free apps that help your customers, it creates qualified leads for consulting.

Above all, do great work. If you're awesome and you can show your customers that you can scale that - without effecting their projects - then they will talk about you to everyone.