Hello, Undisclosed:
This answer varies based on which type of business you're seeking out. As an integrator, it can even vary on the types of systems you typically install/service. For example, Dodge and isqft can be a good source for Access Control jobs, but can seem pretty big wastes of time for video surveillance work.
However, competitive bidding your way to sustainability is tough. For any integrator, the most productive leads come from 'pounding pavement' - meeting regularly with existing customers on future expansion, or potential projects they have heard from peers. Asserting yourself as a 'consultative salesman' is a good approach, if you have the experience and knowledge to back it up.
Introducing yourself to, and cultivating relationships with the local General Contractors or Construction Management Companies in your regions are good, too. Those guys are often responsible for getting video surveillance or other security systems installed, but often do not have the time to formally bid things. At the end of a project, they are in a hurry just to get the project finished - so they hit the Rolodex and call a trusted subcontractor. If you can be 'that sub', you stand to pick up a lot of work.
You should also consider introducing yourself to the 'security consultants' in your area. If you can establish credibility and trust with them, referral work sometimes falls from the sky. Same with your Manufacturer Reps and CSRs. Actively talk to those people, don't just wait for them to call on you.
Security sales is tough. Sometimes it feels like you need to move 2000 pounds of prospects to glean that 1 oz of contracted projects.