One of the best resources I’ve ever found for writing is a site called Magnatunes.
( http://www.magnatunes.com/ )
You might be wondering, A music download site is your best resource for writing? And the answer is yes. I love having music playing in the background when I’m writing, especially if it sets the atmosphere for a scene I am writing, but it cannot have lyrics. There are two reasons for this: 1) I can’t concentrate on my words when I’m filled with lyrics and 2) If it is a song I like I can’t stop myself from singing along, which totally breaks my concentration. (Also I am an embarrassingly bad singer.)
Magnatunes is a fantastic resource that is sort of like iTunes for artists who aren’t going through big production companies to put their music out there. You can listen to all of the music on Magnatunes for free and if you want to download the music, have limited licensing use of the music for things like book trailers, and the ability to embed the music in your website/blog, the subscription is pretty reasonably priced with a 7 day free trial. But like I said, you don’t have to pay for a subscription to just listen to the music, which is what I’d done for a long time before I decided I wanted to download it. Also, the artists get a huge chunk of royalties for their music, more than they might get with producing music in the traditional way.
Their tag line is “We are not evil” and that is kind of awesome.
Most of the albums have no lyrics and are incredibly ambient. There is a huge range of music from relaxing forest sounds to beautiful classical pieces to lyric-less rock’n'roll.

I discovered Magnatunes after playing the Xbox arcade game Braid, a platform puzzle game by Jonathan Blow. It is one of the most enjoyable, philosophically intriguing video games I have ever played and it shows how much you can do with a tiny budget and a passionate one man staff. Braid has a very haunting, emotionally spellbinding soundtrack and it can only be found on Magnatunes. I listen to it a lot when I’m writing.
(I have sample music embedded on my blog if you want to listen that way, or just follow the link to their website. I couldn't embed here. http://www.sommerleigh.com )
Braid Soundtrack: ( http://magnatune.com/artists/albums/braid-soundtrack )
Another more upbeat and cinematic album is Circles by Darko Saric: ( http://magnatune.com/artists/albums/darkosaric-circles )