Stop recommending Gundam Wing. Seriously. All the show has going for it is nostalgia and the fact that the original American showing cut some of the worst plot cul-de-sacs and stupidity out. As it is it's one of the worst Gundam shows out there.

Anyway, I support Tengu's recommendations and don't really see a problem with them. For Steins;Gate you don't really need to know otaku culture that much to see that Daru is a pervy nerd or that Kurisu understands his nerdiness far more than she wants to show and that's really all you need in understanding otaku culture. The rest is purely extras.

Madoka is probably a bit harder, it does heavily relate to a rather inaccessible and often joked about genre. I don't think it is impossible though, as long as he's willing to accept the drama and let it pull him along, then the magical girl trappings will really just be a quirky visual style. Also, who can't love the music?

I can also second Spice and Wolf. It really is an excellent show with not only accurate economics, but also one of the most accurate portrayals of the European middle ages, something that makes me squee as a historian. The heart of it, Lawrence and Horo, also makes for one of the best sets of main characters I've seen.

Shame that it seems to need to be almost completely without anything dirty, otherwise Haruhi would be a good thing to show. Excellent plot and characterization and really, the parts with the girls being dressed far too little most serve to reveal character. It might be an option if you think he won't be liable to jump to conclusions immediately and try to read the situation of the pervier bits. It is also a lot more serious than when it looks at first, though there really are a lot of jokes flying around all the time.

For something completely different. Crest of the Stars and Banner of the Stars, which is basically serious space opera. Describing the setup would suggest a cheesy romantic comedy, but it is ultimately the story of galactic empires clashing and the troubles there comes with administrating such empires. Except for the final season of Banner of the Stars which is sort of a more personal episode for the main characters, but the series wasn't successful enough that later books got adapted, so it kinda ended there. Still a recommendations and basically free from anything remotely ecchi. Unless blue-haired space elves is inherently ecchi, I suppose.