Do the maintenance or look in the yellow pages for a chimney sweep. That gadget referred to above isn't that expensive either. As another reader mentioned, your local fire department has loaner brushes, so it helps if you know the diameter of the flue when you go to borrow them.

 A sweep can inspect the chimney to make sure it's not compromised, esp if you live in a seismic area, or if the masonry is fairly old.

Always burn wood that's been down/dried at least one year. Spruce and birch produce the least amount of creosote. I also remove the 'china hat' off my stack in the winter, as it clogs easily with creosote; it goes back on in the spring to keep the rain out.