Initially inspired by this post over on John's Scion Resources (which is a GREAT site to check out if you're playing Scion).
In thinking about music for Leander (and by extension Malena), I came up with a few things that would fit him pretty well and provide some insights. One song that came to mind pretty quickly was AC/DC's Hail Caesar. The lyrics remind me a lot of the potential intrigue happening behind the scenes for Leander with him being distrusted by Zeus. After all, he's a piece of Athena... A male piece, which was also born of Zeus. Which just might make him as much Metis' son as Athena's, and that might make him the son prophesied to overthrow Zeus the way Zeus overthrew his father. Which Zeus is decidedly against.
Another clear choice for Leander is the Hyperion Overture from StarCraft II (well, more appropriately, from the trailers for StarCraft II). It nods back to his hobbies and his strategic leanings. It also has a rather triumphal and mythic feel to it, which is definitely more where Leander leans a lot of the time, given he's been on Olympus or acting as an agent of the Gods for a while. I also think it has some tragic notes, which probably also fit well with Leander.
Madonna's Like A Virgin is also on the list. If you've read the interaction between Leander and Malena, this is a fairly self-explanatory selection.
Celldweller's Hyperion fits pretty well, I think, with the battle between the Scions and Fafnir, with segments that match up with the different phases of the fight. Similarly, Celldweller's Jupiter fits pretty well for those situations in which Leander steps up from the back lines and suddenly puts a lot of damage into someone. It's rare, but the build in the music seems to fit so well with him suddenly blurring into action.
For Malena and Leander's relationship, I'd use Israel Kamakawiwo'ole's White Sandy Beach of Hawaii. The lyrics speak of soothing dreams of a loved one, which I think is pretty much where Leander is at in that relationship right now. I think Malena would probably be amused that I think the song that would work for her is Meredith Brooks' Bitch. While I don't think of her as a stereotypical "bitch," I think her outspoken and forceful nature could easily get interpreted that way. And she's rarely regretful or ashamed, but she's also very caring and kind when it's appropriate.
The game's theme song has long been the Russian cover of Carry On My Wayward Son by Kansas, so both versions need to rate on this list.