Sundew will catch fungas gnats for certain. I bought one late last year and it was catching lots, but it died back for the winter before I had chance to see if it was an effective method.
My mum reckons that Venus Fly Trap also catches fungas gnats/fruit flies. That suprises me and I'm still a bit dubious, because they tend to catch much bigger flies from what I've seen.
I've seen pitchers in the shop with masses of fungas gnats on the liquid, so they must be able to catch them.
Whether a couple of plants can control them is another matter... I think the question really is how many carnivorous plants are needed to actually make a dent in the gnat population