So far, RedSn0w has been the only publicly released tool that can jailbreak iOS 4.2.1. The Dev Team warned users about the dangers of updating their iOS firmware to 4.2.1 before the RedSn0w beta was released. Around that time, the iPhone hacker, P0sixNinja, said that the GreenPois0n jailbreak would be ready for 4.2.1 around the same time as RedSn0w.
The GreenPois0n jailbreak has still not come out for 4.2.1, a LimeRa1n update is nowhere to be found, and all we have had is a somewhat unstable RedSn0w beta. Luckily, PosixNinja has recently said that the GreenPois0n (most likely tethered) jailbreak will actually be ready very soon. And Geohot could always come out of the woodwork and surprise us like he did with LimeRa1n.
After some drama about a leaked SHAtter exploit in mid-December, the jailbreak developer community has seemed to be a little more divided. Comex, a prominent personality in the jailbreak community, was supposed to be working on an untethered jailbreak tool for 4.2.1. However, it seems he might be saving his hack for iOS 4.3...