Only certain posts to front page?

I imagine there’s either a hack/plugin to do this already or someone has done it, so I figured I’d ask before I try to do one myself.
I’d like to be able to have certain posts I create only show up under the category link. So for example, if I make a custom key that I could set for a post and that post will only show up if a person looks at the category for that post, but the post will not show up on the front page.
Can anyone help with this? Thanks!