This Monday, Apple released iOS 4.3.5, a security update that patches a flaw in its handling of security certificates.
If you're looking to jailbreak 4.3.5, though, here's some good news: "MuscleNerd" of the iPhone Dev Team decided he would check to see if Redsn0w would successfully jailbreak the minor update. You can, however there are still a few pitfalls.
First, the jailbreak only works with the iPhone 3GS, iPhone 4, third and fourth-generation iPod Touch and original iPad. Also, this jailbreak is only limited to a tethered boot with iOS 4.3.5, so whenever you reboot your iDevice, you will need to connect it up to your computer. Lastly, you can't use Redsn0w if you use a carrier unlock.
iOS 4.3.5 is Apple's second security update to iOS in the last week and a half or so. Apple released iOS 4.3.4 on July 15, which fixed the flaw that Jailbreak.me 3.0 tool took advantage of.
If you're on iOS 4.3.5 and are willing to give this a try, you can download the necessary files for Redsn0w and then following the steps on Redmond Pie's website.