I use 1and1 (UK) who seem reliable and trustworthy. You do however have to supply your phone number and address (I doubt there are any registrars that don't require this, but don't quote me on it). Those are required for your domain's whois entry (apart from .uk domains where it doesn't have to be published). I haven't ever been sent anything, and haven't had any phone calls, so I think they're fine on that count.