Lego's range of build-it-youself games help address the problem of what you do with Lego models once you've finished building them. Some of them are very good.
Race 3000 is a car racing game for up to four players. The cars progress around the track based on the roll of a coloured die. The coloured die is modified during the game - each player has opportunities to add more of their coloured squares to it, so their car is more likely to move further. There are two tracks, with obstacles (Lego oilslicks), shortcuts and places where you can swap between the two lanes.
If your turn would land you on top of an opponent's car, you overtake them by moving forward to the next available space that is not obstructed by the opponent car. The "not obstructed" bit is open to interpretation, because the cars overhang several adjacent spaces. If you move between tracks, you do it in a single move, even though it looks like there are two "squares" to cross.
We found the basic set of rules to be slightly ambiguous in a couple of places - to avoid arguments, you need to be clear about your interpretation befor you start playing. Lego positively encourages you to modify the rules to suit yourself, which may help hone your childrens' creativity and negotiating skills.
The squares through which the cars move are the studs on top of the Lego bricks, so can be a bit fiddly for people that need reading glasses.
The box says it's suitable for ages 7+; I'd probably say it's better for 8 or 9 year olds, but perhaps some 7-year-olds would disagree!