Global Graphics & Gifts is looking for card ideas that are traditional or that use humor in a positive way (no insults or put-downs). They want verse for both seasonal and everyday cards, and they accept submissions by email (as attachments) or snail mail with a SASE. Their response time is fast -- typically 6 to 8 weeks. Payment rates aren't specified.
(Thanks to Kate Harper, whose Greeting Card Design blog this market was found on.)