As the news and tweets from the iPhone Dev Team indicates we are going to get more than one tool to jailbreak iOS 4.3 and iOS 4.2.1 this year. The latest is from Musclenerd who has announced the successful porting of Jailbreak Monte to 4.1 Kernel, which will give untethered iOS 4.2.1 jailbreak.
The same Jailbreak Monte will be used on 4.3 to get untethered iOS 4.3 jailbreak. The other major release is Redsn0w 0.9.7 which is again using the 4.1 SHSH blobs to give you the untethered iOS 4.2.1 jailbreak.
Chronic Dev team has also posted a video demonstrating the Greenpois0n untethered iOS 4.2.1 jailbreak achievements and is expected to come soon.