Should I retain copyrights?

Normally, the agreement for the things you're writing is what's referred to as "work for hire"--you do the work, they get the copyright once you've been paid in full. That's very standard and most companies expect that.

Now if they don't have the money you're asking for and you think it's something you could sell to others, I suppose you could (though I haven't tried it yet) give them--I forget if this is the exact right term or not--first use rights instead for a discounted fee. Like it sounds, they get to be the first ones to use it, but you retain the copyright and can sell it elsewhere.

With publications, it varies and the publication usually sets the rights they're buying.

I don't put anything in my agreement about using their work as samples but I do. Maybe that's something I need to look into, the only time I know that people run into problems with that is if they sign a non-disclosure agreement or if it's a big publication.

Ray's got an interesting approach for the ebooks though (one I'll keep in mind Ray, thanks!) and one you could potentially leverage. ie Here's the price with the rights for me to sell it too, but here's the price if you don't want me to be able to sell it too (which is much more).

They may just go with the higher priced option, which gets you more immediate money.

Now, even if you sell all rights, you can still rewrite that piece with a different slant and sell it to someone else who doesn't compete with the original buyer.

Writers who freelance for the big pubs do it all the time. Because at that point, it's a different piece--you're just leveraging the info you collected for the first one. Especially since you may have collected more info than you needed anyway...

Just a thought. But yes, unless otherwise stated, what you write for your clients would be work for hire and the copyright would transfer to them.