As tweeted by developer Ryan Petrich a few hours ago, popular Cydia tweaks FullForce (which allows you to scale iPhone apps for the iPad’s larger screen, something we covered when the first iPad jailbreak came out) and DisplayOut (which mirrors the iPhone’s screen on a TV using a VGA cable) have been updated to support iOS 4.2.1.
DisplayOut is available at $2.99 in the Cydia Store. We highly recommend it as it’s the best tweak currently available to, say, show off an iPhone app on a bigger screen or external monitor.