What kind of workout or stretches can I do to increase my range of motion? I want to be able to do a split (I am quite close).
What kind of stretch should I do?
You need to stretch your hip-flexors, hamstrings and quadriceps.
There are a multitude of resources on how to stretch these areas on sites such as Youtube. Here is a video I found that includes a bunch of good stretches.
You can also do fire-hydrants (and variations), scorpions and iron crosses.