Simple firewall question: Blocking a handful of IPs

[H. Wade Minter]

I'm not extremely comfortable with doing firewall testing remotely on  
production systems, but I need to set up some incoming IP blocks.   
I've got a FreeBSD RELENG_5_4 system with public interface rl0.

I want all traffic allowed unfettered, except traffic from particular  
IPs to be completely blocked coming in.

Can someone show me which ipf rules to use to get that result?

Thanks,
Wade