You can download the Unreal Development Kit for yourself from Big Download, and while you're over there read their blowout coverage, including interviews with Epic Games, Whizzle's Psyonix Studios, and The Ball's Toltec Studios. We've got images and descriptions of both games, along with a video from Psyonix, after the break.
Whizzle was built by the familiar faces at Psyonix Studios (you may remember them from Supersonic Acrobatic Rocket-Powered Battle-Cars) in "less than two months using a two-man team of one artist and one programmer." Unlike the space marine-infused fare you may expect from Unreal Engine, Whizzle is an underwater vertical scroller, in which you play as an "adorable sea creature that collects items and frees allies from captivity." So, like Ecco the Dolphin only with way better lighting effects.
Download Whizzle from Big Download (112 MB)
The Ball began life as an award-winning Unreal Tournament 3 mod by Toltec Studios and has now been ported over to UDK as a standalone download. Epic says, "Anyone authoring mods for Epic's PC games can port their original content over to UDK."
Download The Ball from Big Download (359 MB)