Hi.
The leaders in the market for that kind of software are
Finale and
Sibelius . I work with Finale and it's an excellent piece of software. Sibelius users tend to hate Finale because, according to them, Sibelius is easier to use. I haven't checked that because never tried to learn Sibelius (well, I tried once without the user manual, but when I found the first unsolvable question at the moment, I thought "Why should I puzzle myself trying to learn this if I already know the other one?").
MakeMusic! (Finale's developer) offers a free basic alternative to Finale:
Finale NotePad. Very crippled version of Finale, but maybe useful for you.
Hope this helps.