Hmm, there's a lot of songs that I don't remember that well now because I've seen so many different animes as of yet. But I'll upload as and when I'll remember more
Here are a few of my favourites:
1) Gohan vs. Frieza Theme
2) Rurouni Kenshin - Departure (Thanks Romi for suggesting this anime. Such a wonderful piece of music shouldn't be missed!)
3)Tower of Heaven (piano version) - Fairy Tail
4) Mello's Theme - Death note