ZombiesVsAliens, Shuriken Ninja, and Tools for Phone 7. They just queue forever, then the marketplace crashes. Does this happen to anyone else?
Are you downloading via Zune or WiFi?
If any game or app is over 20MB in size including if it is a large update you have to download via Zune or over WiFi over a normal data connection anything over 20MB will not download.
Presumably this is to prevent heavy data usage without realising it.
if it's a trial, delete it and then download it again.