Marketing to businesses is a very different beast from marketing to consumers.
One difference is the possibility of in many cases obtaining very targeted lists.
If you know who you’re targeting, list brokers can very often come up with a list that very precisely matches it:

companies with 1-5 servers
marketing vice-presidents of florida companies
podiatric practices in urban areas
real estate brokers with 5 or more agents

and so on.
Another difference is there is no “do not call list” for businesses. That means you can effectively telemarket to businesses.
This makes for a killer combination I’ve seen work time and time again:
1. Targeted mailings repeated to a very precise market.
2. Telemarketing to the same companies.
It requires a well-oiled machine for this to work well, but the two – mailings and calls – work together. The mailings (usually postcards, sometimes interspersed with other pieces) remind people of the calls and vice versa.
One key element is the mailings repetition. Don’t do a one-time mailing and expect a result. You have to mail over and over to the same businesses.