There are a lot of useful apps already available in the app store and I don't want to reinvent them just because i think they'd be useful to be part of my app. So I'm wondering whether it is possible to sell them from within my app, whereby the user can purchase them without leaving the comfy confines of my app. Any idea about this? Or will the user always have to head over to the App Store to get their hands on them?
On a side note, it would be nice if i could get some commission for selling them within my app (can't imagine Apple would allow that though).
No this is not possible. Best you can do is redirect the user to the app store app from within your app to the app the user wants more info on.