One of my favourite things about the Mass Effect games, particularly the third, is the gorgeous sci-fi vista of a new alien world as you swoop in to land. I screenshotted my favourites back when I played through, and I'll embed them here for your approval. Click the button on the top right for a nice wallpaper. No plot spoilers if you haven't played it—there's one location you'll recognise from earlier in the series, but I don't think it'll surprise anyone that you go back there.
If you have any favorite Mass Effect screenshots of your own, link us to 'em in the comments. imgur is probably the simplest way to upload.