I've been meaning to start a thread about this for ages and Razgon's thread has reminded me. Blindsight, by Peter Watts, is a book about first contact. The plot is so fantastic that I won't say anything more than that, but I'll say a little about the book. It's very hardcore science; there's no messing around here. If it's in the book it's either real or widely believed to be achievable. In fact the author is a biologist and there's a lengthy discussion - with references to papers and books - at the end. There's only one fantastical element but even that has been put into a "what if" scientific context.
So, hyper-realistic then, but also set in the future so there's a lot of Really Cool Technology too. You can tell the author is a scientist, and if you have a scientific background or even just an interest in science, you'll find an ocean of amazing stuff to immerse yourself in with this book. The plot itself also has some dramatic moments, excellent dialogue, and is generally just a bloody good read. Its characters are very interesting to say the least, but I won't say any more about them.
I don't know if a first contact book has been done like this before, but if it has I haven't read it. I couldn't put Blindsight down and I've read it at least half a dozen times now.
I wanted to write more but dinner's ready. The link is here
for the full novel in HTML, but there are links at the top of the page for other versions including PDF. You can't argue with the price, so if you have any love for sci-fi go grab it now. It's a bloody amazing book.