One has to be careful not to just include any story with a 19th-century or early 20th-century setting. There is nothing in the least steampunkish about The Gunfighters or Timelash, for instance, despite the supposed 19th-century setting of thee one and the presence of the young H.G. Wells in the other (and one would have to stretch a long way to include Pyramids of Mars or Black Orchid). But I think it's pretty clear that the following could be considered at least a little steampunk:
Evil of the Daleks - Victorian inventor produces time machine - what more could you want?
Talons of Weng Chiang - granted that the technology itself is not indigenous to the 19th century, but the attitude to Asian people certainly is. (And the recent Big Finish sequel, The Mahogany Murders, is definitely steampunk.)
Enlightenment - the sailing ships may be from all parts of history, and the centre of historical gravity probably nearer the 18th than 19th century, but really, I look at it and I say "steampunk!"
Tooth and Claw - rather than The Unquiet Dead, even though they both have 19th-century settings, because T&C has Queen Victoria and a telescope rather than ghosts and leaking gas.
(Imagine if The Red Fort had ever been made...)
Various thoughts about audios and books, but I'll pause here.