How can I normalize mRNA samples for sequencing?
I found the link to a commercial product by Evrogen here:
http://www.evrogen.com/technologies/normalization.shtml

They claim their method is compatible with nextgen sequencing platforms:


  cDNA normalization using duplex-specific nuclease (DSN) is a highly
  efficient approach that can be applied for normalization of
  full-length-enriched cDNA (Zhulidov et al., 2004; Zhulidov et al.,
  2005). The resulting cDNA contains equalized abundance of different
  transcripts and can be used for construction of cDNA libraries and for
  direct sequencing, including high-throughput sequencing on the next
  generation sequencing platforms (Roche/454, ABI/SOLiD or
  Illumina/Solexa).


And the most up-to-date reference seems to be this Curr Protoc Mol Biol. paper by Bogdanova et al.:
http://www.ncbi.nlm.nih.gov/pubmed/20373503