[SolarfluX]

https://solarflux.org/pf/pf-tips (read this BEFORE reading the FAQ below and you'll see that the FAQ and its examples need to be updated!)
http://openbsd.org/faq/pf/

[elmore]

I'd also add that several of the most common problems people new to pf have, have been posted and answered in the forums here. Make sure you read the existing threads as you're liable to find many of the common gotchas there.

Good Luck! :)