Are there any LEGO base plates that are compatible with Duplo?
A regular LEGO base plate will work with DUPLO bricks. As demonstated in this question, the two systems are compatible in a number of ways. Here's an example of System base plates with DUPLO bricks attached:



It should be noted that not all DUPLO bricks will be able to connect to a System baseplate. Some examples of incompatibility are round bricks and some of the minifigs and animals. In order for these to connect you'll need a DUPLO brick or baseplate on top of the System baseplate.