This is one of my favourite talks, written for PHP Barcelona last year, about how to consume web services from PHP. It covers data formats, different ways of handling HTTP, the different service formats we're likely to encounter and also gives some tips on troubleshooting ... all in the space of an hour!

Blog: http://beta.lornajane.net/posts/2010/Working-with-Web-Services-Froscon-2010

http://www.slideshare.net/lornajane/working-with-webservices-5031166