Any Nitric Oxide product. Also, im sure caffeine/ephedrine and pretty much most stims will give an increase in vascularity. I will give you two words though that are tried and true methods.
The element in Supplements that gives vascularity is always arginine-based, i.e. No-explode, Nitrix, Xpand, etc....Arginine gives great vascularity to allow extra nutrients andoxygen to pass through your veins, providing muscle pumps and growth.
Just dont take to much arganine/AKG. I loved the vascularity I was getting when I used my first supplement of this type and doubled than tripled the dosage, I ended up getting crazy vertigo and passing out a few times. More isn't always better than enough.