Beginner hardware
stub
The best, first advice is to check that your camera is compatible with zoneminder's motion JPEG (MJPEG).
You should read the Documentation. The developers spent and continue to spend a great deal of time writing it... you should spend at least a little time reading it. Specifically, read the part about shared memory.
Recommended IP cameras
Axis brand cameras are a good choice, but expensive.
BSIT are really cheap but also not the greatest quality.
Camera quality varies greatly, both in actual image quality and in operational reliability. Remember that you often "get what you pay for." Cameras from high volume manufacturers may be subject to software/hardware compromises that lower cost at the risk of breaking functionality and/or compatibility with standards.
Avoid cameras that require 1.24(aka: mpeg video) because it make things harder for beginners.
One place to buy cameras:
