The evolution of Southern American English

SAE also modifies the English auxiliary system by allowing for the use of more than one modal in a verb phrase. For instance, for most Southerners “I might could leave work early today” is a grammatically acceptable sentence. It translates roughly as “I might be able to leave work early,” but might could conveys a greater sense of tentativeness than might be able does. The use of multiple modals provides Southerners with a politeness strategy not available in other regional dialects. Although no generally agreed upon list of acceptable multiple modals exists, the first modal in the sequence must be might or may, while the second is usually could, can, would, will,should, or oughta. In addition, SAE allows at least one triple modal option (might shouldoughta) and permits useta to precede a modal as well (e.g., “I useta could do that”).

Read more here, and thanks to the ever-excellent www.geekpress.com for the pointer.  The comments are open for other good examples.