There's "Greek Grammar Beyond The Basics" by Wallace -- a lot of people recommend it but I didn't like it that much, but it's certainly worth taking a look at it to see if you'd like it.
For stuff that's available online, there's the "A Grammar of the Greek New Testament in the Light of Historical Research" by Robertson. It's what I turn to first when I have trouble. I like it -- it's very detailed and comprehensive (but to nitpick, it does take the 8-cases approach, which I'm not a fan of). I also occasionally use "A Grammar of New Testament Greek" by Moulton.
From what I've seen of people's opinions, I don't think there's a widely recognized best for NT Greek. There are lists like the one at http://www.ntgreek.org/books/grambook.htm
and you might want to check out the other grammars but I don't think anything will be a huge improvement on the Blass grammar, except in terms of personal preference.
(Smyth's grammar is very good, though, and I do wish there were something just like it for NT Greek.)