Pavane has a program called Harmony. I didn't get on with it last time I tried it, but he clearly likes it (because he wrote it ;-) and I think others do too.

Personally I use Melody Assistant. You can use it for free and it nags you to register, but registration is dirt cheap so it's worth doing if you're using it a lot.

If you go back through the archives searching for "notation software", you'll probably find stuff. It's come up a number of times before.

Graham.