FreeSound.org can help you!

[Janus]

When I'm making my music, I'm using this site very often: http://freesound.org/
It's great because you have some completely free sounds which can be great for making your songs better. You can find a lot ambient sounds, frequencies, melodies etc. and you can also upload some of your work and share it with other people.

[AlienXXX]

Music uploads are not allowed at Freesound - but since ambient music often lies in the border between music / texture / sound collations... You may actually find that many ambient pieces would be accepted.
In any case, please note that the purpose of Freesound is to be a databse of SOUNDS. So uploading music is not encouraged and submissions of full musical pieces are likely to be rejected.
However, drones, tones, textures, synth pads... all kinds of sounds, really, will be accepted.

Another important point is that if you are into sound synthesis / creation / engineering (whatever you want to call it) you may find the site has a lot to offer: sound examples, techniques, forum discussions, and expertize from members. You can even post sound requests, which are often answered

[Janus]

Yeah, I didn't mean that you can download or upload a full song, just some part of it (melodies, textures etc.)
For full songs (jingles) you have; http://audiojungle.net/

[MetaDronos]

Any FreeSound members here? I am one, be my guest at http://freesound.org/people/Trebblofang/

[AlienXXX]

I am also AlienXXX at Fresound.org

[Duckett]

james duckett @ Freesound