We've been doing a lot of work recently with the Linksys WRT54G, and they certainly make cheap and versatile linux APs. One problem however, is they need a fair bit of protection if they are to be used outdoors.
One group that's had success using WRT54Gs outdoors is sveasoft - and they've produced a fantastic writeup dedtailing how to armor the WRT54G for outdoor use.
Read the full write up at http://www.sveasoft.com/modules.php?name=SveasoftArticles&op=SveaReadArticle&id=1
