The official Lego games are a must. I will use their customisable dice, their inventory system and their handy little monsters for Brickworlds. Heroica is a simple baordgame that can be played with young kids. Each box is a different dungeon and you can put them together for some epic adventuring
If you can bear reading the ad-riddled page, the Lego Dungeon Crawl game uses an interesting colour coding system and a full session story with photos. I still have to read the rulebook.
BrickQuest is another dungeoncrawler, with amazing looking builds and rules akin to the old Games Workshop game HeroQuest. It's pretty simple but has races, classes, spell lists and a bestiary. The only thing is, you need a whole lotta bricks to play. I love their brick character sheet.
I also found a strange little experiment hosted on Flickr and called, *cough* Brickworld *cough*. Apparently it's like a play-by-forum game, only with photos. Look here for an example.
Last but not least in the tactical department, there is Small Wars, a game designed by Croc himself for Corgi, one of the competing brick brands. Easy and fun, it will certainly inspire mass combat rules, should Brickworlds need them.
Are there any other games out there I should check out? Please infuse me with your bricky wisdom in the comments.
Edit 09/10: Denis pointed me to Brikwars, which looks like a very comprehensive battle boardgame. They also have links for a lot of brick-based games.
Photo by Chris Xenyo on Flickr.