I have to say, I haven't had time to look around at other people's blogs, but if you find any better mix of facts and speculation on the Upper House election aa well as the overall political background by a single individual than Observing Japan, let me know. For example, this July 14, seat-by-seat analysis (which I just noticed) requires a granular perspective of a real pro.
Addendum: Note that for the single-seat races, the July 18 Yomiuri called Iwate, Yamagata, Yamanashi, Mie, Shiga, Nara, Tokushima, and Okinawa Prefectures for the DPJ, and Gunma and Yamaguchi Prefectures for the LDP. (The rest were still tossups.) The ten calls are identical to the ones Japan Observer made in his post four days earlier. So the Western media could do worse than take his other 18 calls seriously as well.