Apps not downloading.

I have an iPhone 3GS running iOS 4.1. I've tried downloading an app and it just says 'Waiting...' I thought it was a bug that was going to get fixed. That has been there for days.

I tried downloading another App today and the same problem. I then realized it's not the developer, but the iPhone itself. I can't install it again as it says 'Installed' and I can't delete the app when I hold it down.

Is anybody having the same problem and how could I fix this?

All help is appreciated. Thanks.