I have known two Welsh x Quarter horse crosses. They were very spunky little things! The intention was to produce a larger children's mount but they both proved to be quite the handful. They were pretty easy on the eyes, though. Nice and refined like a welsh and with flashy gaits, but with more muscle and size. One was the most amazing dappled grey for a few years when he was younger. Prettiest color I've ever seen!
There's also a Paint x Fjord yearling for sale down the road from me. She didn't turn out well I'm afraid. She looks kind of like a potato with spots O.O
My personal favorite is Saddlebred x Belgian or other heavy draft. It sounds awful, but for some reason the horses are usually amazing. I think there's even a new breed founded on this cross; the Georgian Grand or something like that. Love, love, love it!