Yahoo! Hacks

Most of these are written based on APIs described at developer.yahoo.net.

buzz.progphp.com
A Buzz Index, Image Search, News Search aggregator demo.
(patience - can be slow)
flickr.progphp.com
Similar to Buzz but using Flickr as the image backend
g2f.progphp.com
Gallery2Flickr image transfer application. This one is full of nasty hacks.
Flickr PHP5 API
Flickr API rewritten and expanded for PHP 5.1
simple_rss.php
Tiny RSS/ATOM reader for PHP 5.1 (Not really Yahoo! specific, but very handy to read Yahoo! RSS feeds)
Unsafe Search
This is the opposite of SafeSearch. Instead of removing unsafe results from the set of all results, this removes safe results from the set of all results. Hours of fun and sometimes rather disturbing searching can be had with this one. It was written for very benign reasons though.
Earthquake Map Mashup
The last part of my very simple Map API tutorial at http://toys.lerdorf.com/archives/35-GeoCool!.html. It just grabs the earthquake data from USGS and sticks it on a map.
V3 DHTML Yahoo! Map
Version 3 of the Yahoo! Maps DHTML API. You can feed it a geocoded RSS file directly now, so the above earthquake mashup becomes: http://lerdorf.com/ymap?q=http://earthquake.usgs.gov/eqcenter/recenteqsww/catalogs/eqs7day-M2.5.xml