There are a lot of sites selling sheet music - and then there is ChorusOnline.com that just delivers a better product!
It might be a little more expensive but the quality of the sheet music and the rehearsal files makes it so much more worth bying it there.
Strengths
The rehearsal files and the opertunity to search in 5 levels of difficulty (other places its just 3)
Improvements or suggestions
Only one more thing - more arrangements:-)