Note: There is NO unlock for iOS 4.3 yet. If your iPhone relies on a unlock, DO NOT update to stock iOS 4.3 yet.
As reported by Redmondpie, Jailbreak for iOS 4.3 is now available. You can use Snowbreeze 2.3 for Windows and PawnageTool for Mac to jailbreak your iphone 4,3Gs,3G running iOS 4.3.