Peter writes The best free PHP IDE has sold out to Nusphere (The same people that have "Aquired" MySQL), and is now available at http://www.nusphere.com/products/phpadv.htm. Well, at least it will have the funding it needs and could become one of the best out there now.
Peter also made note of a note in the DevShed forums that talks about a few people wanting to start work on an Open Source PHP IDE...so if you're interested, drop on by and give it a look.