What could be more simple than a one-layer card? Certainly saves time if I don't have to cut up lots of layers.
Here's my most recent thank you card:
I've used a beautiful new stamp from the "Fresh Vintage" stamp set - available as a free gift during Sale-a-bration. The colours are Bravo Burgundy, More Mustard and Old Olive. The "thank you" sentiment is from the "Teeny Tiny Sentiments" stamp set.
Markers are a great way to get lots of colours onto a one-layer card.