The fourth beta version of the iPhone SDK includes Xcode IDE, iPhone simulator with Open GL ES support, Interface Builder, Instruments, frameworks and samples, compilers, and Shark analysis tool.
You can download the SDK update by logging into the iPhone Dev center and clicking the download link.
Thanks to everyone who sent this in!
9:31p New beta build is called 5A258f
9:31p SDK download is 1.15 GBs
9:32p No word yet as to whether pwnage will work with the new firmware--probably not. The last time it took almost a week for pwnage release to catch up (that was version 1.1).
9:34p We're getting tips that Apple is sending out e-mails to developers enrolled in the SDK beta. The e-mails include the same message as above,
9:35p Firmware sizes about 200+MB each for iPhone and iPod touch
9:36p Apple continues with its beta pre-installation advisory. Testing devices may be locked permanently into testing mode.
9:37p If you're new to the SDK program, make sure you phone has been pre-activated with AT&T before you attempt to load the beta software. Once the beta firmware is loaded, you may not be able to activate with AT&T's network.
9:38p No word yet on any other changes, other than those mentioned in the e-mail / website.
9:39p Apple just put the release notes on their website. You can find them here: http://developer.apple.com/iphone/library/navigation/index.html
9:40p Code signing is now ENFORCED by Apple.
9:41p SDK no longer uses the Aspen code name for the simulator.
9:42p Audio Toolbox got a big load of new stuff
9:42p NSXMLParser support
9:43p UIFont is re-done with ascender and other professional font support that has been long missing.
9:46p Please keep sending in info as you find it out everyone! We really appreciate your tips. If you need anonymity, check out our tip line. Thank you to everyone for the great feedback so far!
Update: A blue and green birdie sang in our ear about the UIApplication delegate class: "There are definitely some very interesting methods added to UIApplication's delegate, including methods for badging the Springboard icon, and methods related to gaining and resigning "active" status - seems like background apps may be permitted somehow."