I hope this doesn't sound Frankensteiny. Poodles and spaniels are routinely cross bred so I don't see why others can't, within reason.
Pointers, especially GSPs and Weimaraners, are very sleek, elegant animals and I like the boisterous affection of Labradors. A cross of these two could produce a handsome dog that isn't prone to getting fat !
Obviously, a Jack Russell - St.Bernard cross is a non-starter.