There are definately some US Airlines who permit pilots of other US and a select few National State Carriers (BA comes to mind) access to the jump seat.
In the UK there are a few airlines who positively encourage flight deck access, but the process is pretty long winded and, departing from the UK, we often have to pay hefty security taxes - on "low cost" flights these are often substantially more than the air fare.
A lot of ATC employers positively encourage famil' visits but balk at the idea of the substantial costs involved.