Vanity combination (relegated to the notes)

So what was I thinking yesterday when I played 18...Ng4!? in the position below?  Yes, taking on f2 with check is threatened, but there is no mate, and it seems that White could play 19.dxc6 "for free." Don't let Rybka decide for you: use your noggin. Post the critical variation(s) in the comments.

In the post-mortem, my genial opponent (a NM from Virginia) and I suspected that the move was possibly not the best, but definitely the most fun to play in the last round.

NM Adarsh Jayakumar (left) and a Cro-Magnonesque blogger desperately trying to stay awake after Yet Another Giuoco Pianissimo

Courtesy DeKalb Chess