I like "Flash Video for WP7" quite a bit - it lets you play videos from some streaming servers, e.g. PutLocker among others (used to be able play Megavideo and VideoBB when they were around...). I'd say it's pretty good in value, you can download those videos to your phone, and the developer is working around the clock to keep it up to date to play those streams, as well as expand to other servers.
YouTube Pro and Next Gen Reader are also pretty nice, so is Fuse, that LiveTile Scheduler app that syncs to your Windows Live Calander and presents scheduled events on Live Tiles. You could also pick up one of the Pandora apps.