The first of the Blizzard-made maps is a humorous creation called Aiur Chef, an eight-player free-for-all in which players collect “ingredients” from around the map that are required for recipes, which each grant various rewards, such as points, items, and special powers. You compete against an opponent for a high score, and while you can’t kill each other, you are able to hinder the collection of ingredients through effects like stuns and slowing effects. Each of the three rounds has a “theme ingredient,” and you can see units running around carrying pots and drumsticks and rolling pins. There’s a new UI window showing which ingredients you have left to collect.
Another custom game, titled Left 2 Die, is based on one of the missions in the single-player campaign where players were swarmed by hordes of zombies every night, using daylight hours to rebuild and go on the offensive. Blizzard received enough positive feedback about that particular mission that they decided to go ahead and make a standalone version (tipping their hat to Valve's Left 4 Dead in the process). It's a co-op game, and as you mow down zombies you collect Zerg Biomass to buy upgrades for your army (upgrades that are shared, so you don’t have to worry about competing with your partner). There are new zombie units to contend with, inspired by those in Left 4 Dead, but adapted so they make sense in an RTS.
Next is a game called Starjeweled, which sections off half of the UI into Blizzard’s interpretation of the popular Bejeweled puzzle game. When you match a group of similar symbols, they disappear and grant you resources to spend on units, which then go out and try to attack an enemy base.
Perhaps the most notable of Blizzard's custom games is what they call Blizzard DOTA, based on the hugely popular Warcraft 3 mod Defense of the Ancients. In teams of five, players will control Heroes that can buy items, gain experience and level up, while the map constantly spawns waves of monsters from both bases. The heroes will be a collection of notable Blizzard characters from various games.
During the panel about the map tools, the Starcraft 2 team was very focused on introducing map makers to the basics of development. They talked about the necessity of making the first few minutes of a custom game easy to understand for new players, since getting massacred while being utterly confused is not an experience most players will want to repeat. They also encouraged map makers to take a more active role in soliciting and responding to feedback. Blizzard relies heavily on iteration, and they think the community would benefit from doing so as well.
Blizzard was insistent that the custom maps they will be releasing are part of an ongoing process to keep making new maps and custom games for players. One of their big goals for the immediate future is to keep demonstrating what their map editor is capable of and getting assets in the hands of players to facilitate building. To that end, the custom games they’re building will be unlocked, so the community will be able to look at the internals and modify whatever they see fit. (And speaking of security, they're working on better safeguards to keep people from copying others' maps, should the creators wish to keep them private.) Another reason they built the maps was to see in what areas the editing tools were lacking, so they could continue to add and streamline functionality.