One of my favorite Merrie Melodies series is Daffy Duck's Duck Dodger in the 24 1/2 Century. I just love the mix of sci-fi and comedy elements, it always made me laugh.
Here's a great poster of this series created by Tom Whalen for Mondo Tees. Unfortunately it's already sold out, but at least we get to look at it.
What's your favorite Looney Tunes character and series?