If you consider Shinku as being the female lead, then Rozen Maiden fits too.

Quote from calstine

If you consider Shinku as being the female lead, then Rozen Maiden fits too.

Ooooo, thanks! This looks really interesting.

Does One Piece count?

Polite bump.

Any eligible others? 😛

I live for platonic love/best friendship/close partnership. This is a very rare occurrence, so there aren't many to add, but I'll have a go:

The Friendly Winter
No. 6 (Novel)
Ansatsu Kyoushitsu
Kataribe no List
Hito Hitori Futari
Barakamon
Jiraishin -- But they're not friends, just partners at work.
Tom Sawyer
xxxHoLic -- Well, not so much friends as employer-employee, but she really does adore him in her own way, and he, her.
Hinamatsuri
Mozart wa Komoriuta wo Utawanai
Kare no Aijou no Hakari
Annarasumanara
Pandora Hearts -- Gil and Alice, though Gil is the tritagonist, not the male lead. Oz (the male MC) is obviously romantically interested in Alice, and she in him, but it's very subtle, and Gil is almost as important to them as each other, so...
Tsubasa Reservoir Chronicles -- Sakura and Syaoran are a couple, of course, but Sakura's relationship with Kurogane and Fai is very much this.

Also, in anime:
K (yes, the title really is that one letter)
Another