I have several OSTs on my MP3 player, and people always give me puzzled looks when they notice it. I'm glad I can share some here.
Now I'm pretty sure most of the music I'm gonna post was already posted, but hell, I'll post it anyway, because I think they deserve it.
So, first off, let's start with something calm. Those musics are from the game Endless Space.
Here's a link where you can listen to most of them:
I suggest listening to "Deafen Dawn", "Flawless Theory", and "Beneath the Strings", at least. I think the entire OST is good, with a few amazing tracks, but that's just my personnal advice.
It's a turn-based strategy game set in space, and the chill music really fits. Also, a strong factor that made me like the music, I think, is that the music scales depending on your actions. If you look at the entire galaxy, it will be very calm, but when you zoom on a solar system for instance, it will add a few instruments. It doesn't sound much, but I guarantee it really adds to the atmosphere.
In the same vibe, the same composer made soundtracks for a game called Endless Legend. It's also pretty chill, but this time it's set in a Fantasy setting. It's worth taking a shot.
I'd suggest to try "Dusty Strings" or "From Dawn To Dusk". I'd like to suggest more, but I'll just let you work your way through the playlist.
Now, for something a bit more energic: The Ace Combat: Assault Horizon music has amazing tracks. Some tracks are just "ambient" tracks with no real music, but some are really packing a punch. Here's a few examples (Sorry, couldn't find non-Youtube links):
If you liked those, I'd suggest going for "Dogfight", "Fighter", or "Shall Defend".
I'd like to name a few other soundtracks, but I feel like I'm going to spam the board if I do. So... Yeah.