You must give Pandora a chance if you like music. Free
If you have a lot of passwords or sensitive items to store, try Lockbox. There is a free version.
If you are on Twitter, try Twitterrific. There is a free version.
Wild West Pinball, if you like pinball games try this. Its free.
Distant Suns, you said you like space, this will be a good toy for you. There is a free version to play with.
Urban Spoon, can't decide where to eat, give this a go. Its free.
Remote, If you listen to music on iTunes, this is a must. Free.
Yelp, restaurant reviews. Free
There are a lot of apps to choose from. Palm Pre fans say that half of them are fart apps. I think its more like 38.3% Fart apps. Finding new ones is part of the iPhone fun! Let us know if you find any other good ones!
Hey I must admit I hadn't thought of looking for an app on astronomy and that's weird because I have a star map on the ceiling of my room.
So did a bit of research, there are many serious and fun and some also have reviews (I'm no expert but this link should drive you to a search results page) http://www.iwikiPhone.com/search/node/star?page=2
If it doesn't you should look for StarWalk, nice app!
I have a lot, but my favs are:
TipStar (thinking of paying for one)
Twittelator Pro & SimplyTweet (lite version are free, but I have the paid; $4.99 for both. ST has push)