In my experience many inkjet papers can be scored including RC papers. Ilford has dual sided RC versions if you need a more glossy surface. Lustre Duo. Smooth Lustre Duo. Sihl distributes a dual sided RC glossy too.
Matte dual sided are more widespread, from the inexpensive Red River Aurora Natural to a range of Innova and Hahnemühle qualitities. Hahnemühle will introduce a new one at the Photokina; HARMAN Professional Inkjet by Hahnemühle Matt Fibre Duo. Moab is mentioned already, Epson and Museo can be added, Tecco has one too (could be a Moab clone though).
The 190 grams Moab Entrada Rag Bright samples that I have here in a multibind map show yellowing at some edges on both sides of the paper. Light most likely destroyed the OBA dyes in this case. I would avoid the Bright version for any prints including books.
Met vriendelijke groet, Ernst
340+ paper white spectral plots:http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
update july 2012: Moab changes, paper sorting by name