One of the best episodes of the Fifth Doctors series was Kinda (though one of my friends prefers the sequel episodes Sorta and Maybe). It featured some very creepy scenes and gave Janet Fielding a chance to really show what she was made of as an actress. A figure for this would just be a standard Tegan figure with an extra red mouth and a snake on her arm. Not much, but for fanboys like me it would be a lovely thing to have!
15. Haemovores
These guys only showed up in the classic story The Curse of Fenric, which is truly excellent in the directors cut version and acceptable in the broadcast version. Theyre basically a group of vampire creatures (though not the same as actual Vampires, which the Doctor encountered earlier), and wear various different period costumes. That last part could make for a great set based around this story. Put in Ace, the Russian guy she fell in love with and a pair of Haemovores and you have something very, very sellable!