Here are some of my favorite sites.

Professional:
A New Horn Concerto: www.polyphonic.org/
an article written by Jon and Laura - Part One | Part Two

Lyric Opera of Chicago: www.lyricopera.org/
Grant Park Music Festival: www.grantparkmusicfestival.com/
Chicago Philharmonic: www.chicagophilharmonic.org/
Music of the Baroque: www.baroque.org/
DePaul University School of Music: music.depaul.edu/

French Horn:
Composer Jan Bach: www.janbach.net/
Equilibrium Records: www.equilibri.com/recordings.eq
Collection of excerpts: www.hornexcerpts.org/
Classic horn site: www.hornsociety.org/
Pages of horn classifieds: www.hornplayer.net/
Robert King Music Sales:www.rkingmusic.com/

Interesting sites:
Daily Journal of Art, Culture and Ideas: www.artsjournal.com/
WFMT Radio: www.wfmt.com/
Playbill Arts: www.playbillarts.com/
Kitchen Design: www.jeanstofferdesign.com/
Gardening: www.swallowtailgardenseeds.com/ / www.whiteflowerfarm.com/
Motley Fool Investors: www.fool.com/
Music blog from someone that thinks "outside the box"
Adaptistrastion www.artsjournal.com/adaptistration

Many thanks to:
www.kedrika.com/
www.blueeggcommunications.com/
www.kendephotography.com/