Enter the Geronimo and Thea Stilton series. Even here they have divided the books into two categories - Geronimo for the boys and the Thea Sisters for the girls. But they remain significantly less gendered than what else I have found. The stories are action/adventure. In each one Thea or Geronimo - employees of their family's newspaper business - track down missing people, find treasure, or explore scary houses.
As much as my boys enjoy the plots - and for those who are leery of too much tension, these have not bothered Boy2 who tends to be very sensitive to scary things - the best BEST part of the Stilton books is the actual text.
As I have said, my boys are visual. They like the pictures. So a page with all black and white text still seems a bit too boring. But the creators of this series had a great idea. The font is far from standard. According to The Geronimo Stilton News Site they use "nontraditional fonts and colors" as part of "Visual Literacy." Whatever phrase they use to describe it: it works for my kids! In a big way! They love to see the words played out on the page.
If I could find more series like this I would snatch them up in a heartbeat. Right now it is the only thing Boy2 is reading. He even approached the school librarian and asked for a harder book than what she had put out for the kindergarteners. He mentioned Thea Stilton and read a page to her before she would let him take it out to prove he could read it.
From their site I just learned Geronimo Stilton is a translated Italian series. The Italians are doing it right. For early literacy I love love love this series!