um warchalking.org
pringles cans work ok.. so far our soup can ones work well too.
http://www.turnpoint.net/wireless/cantennahowto.html
or the more notorious one at o'reilly:
http://www.oreillynet.com/cs/weblog/view/wlg/448
i can't afford to test my pringles can as of now but the soup ones are doing fine @ ~ 800ft through trees, open air, and maybe a house or two. 5-30% packet loss depending on how many people have their wireless phones or microwaves or whatnot on in between.
using 802.11b d-link access points.