As I was spoofing vintage travel posters yesterday, I really should mention the king of the medium - Steve Thomas. I love his retro Star Wars inspired travel posters. Here are a few of them:
He also does travel posters, T-shirts logo designs and all manner of retro artwork. It's lovely stuff. And there's a great sense of humour throughout it all.
His website is here and his blog is here. He has a shop too at Zazzle.