Bus enable integrated circuit
The 74HC244 is the typical device for connecting to/disconnecting from a bus. It's an octal tri-state buffer (or rather a dual quad buffer). You'll need the tri-state feature to disconnect completely from the bus. The gates would set the bus high or low, but that wouldn't allow another device on it.

But since you're talking about a data bus you probably want a bidirectional buffer. Then you can use the 74HC245.  

  

You have a DIR pin to control the direction and a /OE which can make the buffer tri-state.  

edit
JustJeff mentions the 74HC374 octal tri-state D flip-flop. (Note: I'll talk about the 74HC574, which is functionally the same, but has a more logical pinout.) The 74HC574 is indeed an interesting part, and a classic since the SN74xx series. While the 74HC245 will give you a tri-state buffer, the 74HC574 has a memory function too, in the form of an octal D flip-flop. Great to make registers, and through the tri-state connection to the bus you can route your data flow easily.
There's a drawback to this, however. The register's output is only available to the bus, so all communication would have to pass there, so that the bus will become a bottle-neck. Therefore I think it's better to replace the 74HC374 by a 74HC273 octal D flip-flop followed by a separate 74HC244 tri-state buffer for the connection to the bus. That way the register's output is also available internally when some other signal occupies the bus. (I don't know if there's a function compatible part with the more logical pinout. You may also use a 74HC574 with /OE hardwired to ground.)