I recently bought 2 of these, they are very light and easily clip to the music book.
http://www.musiciansfriend.com/srs7/g=home/search/detail/base_pid/815600/

You really need one for each page of music.

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Graham
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Graham, Korg Pa1000, Korg G1 Air, Countryman E6, Roland BA330, 2 x Roland CM-30, , Mackie SRM150