While MusicReader has an automatic half-page view, for some pieces of music that doesn't always work well, particularly if you're working with scores that have large numbers of staves in each system (choral music, chamber music, etc.) or odd numbers of systems per page.
The full, professional version of Adobe Acrobat provides cropping tools, but if you're reluctant to invest several hundred dollars for the program, you might want to check out two applications by A-PDF: A-PDF Page Cut and A-PDF Page Crop. Each program is $27, a significant savings over the full version of Adobe Acrobat.
This tutorial demonstrates how you can use both programs to first cut apart music pages, then crop off the borders to maximize the view of the music on your computer screen.
A-PDF Page cut can be found here: http://www.a-pdf.com/page-cut/index.htm
A-PDF Page crop can be found here: http://www.a-pdf.com/page-crop/index.htm