HDD/SDD Encryption software?

Hey all,

I've been looking into HDD/SSD encryption for my laptop.
One, to keep my data/details secure and two, to keep my clients data/details secure.

What is the best route for this?
I have been looking at TrueCrypt for this and I know there's some other ones, but I forgot their names.

So what do you lot reccomend?
I'm wanting something that will make my HDD unusable to anyone trying to get info off of it without my consent either via my own computer or taking it out and reading elsewhere.

How does it encrypt it?
What are the risks involved?
What about files being copied from encrypted HDD to unencrypted, are the files themself encrypted in anyway?

I'm completely and uterrly layman/noob here.