Grab a Vectrex if you can snag one. The prices have gone up on these recently but I can tell you that they are absolutely worth it. Last time I checked, the Multi-cart is available on e-bay right now so that might be your first stop. Just don't let the prices scare you away. As was mentioned, they are still out there at a reasonable price.
7800 would be a nice pickup as well. I have loved some of the ports to that system and its ability to play 2600 games could save you some space and connections.
I agree that TG-16 would also be a nice addition. I have been looking to snag one of those myself.
Good Luck
Bob














