MMD, LTD  Whoops! There went the only plus to this program: the fact that it was free.  
(Version R1)

THE ARCTICMAC  If what you are looking for is basic point-and-click music notation software, NotePad is reasonably good. It's free, and it gets the job done for basic stuff.

You can't do anything like key/time changes, and you can only do basic rests. Grace notes and trills are out, as well.

In addition, it's a bit of a drag to run, at least on my old iMac, as it tends to be slow and less responsive than one would hope.

So, in other words, great, if you want to write out "Twinkle, twinkle, little star", but not good for much that's longer or more complex. But it's free, and it's point-and-click. You get what you pay for.

If you need more advanced capabilities for typesetting, I highly recommend LilyPond (just do a macupdate search). It uses text-based input to create beautiful, complex scores, and, is therefore (provided you are willing to learn the syntax) an excellent alternative for those who would like free, advanced music notation software.  
(Version 2006)

ANONYMOUS  Great. I'm a professional musician and find this useful.

As for the critics below: Didn't you see the name - Notepad? If you have a notepad or notepad widget for text etc. you don't expect it to be a full word processor? (btw even some notepad widgets costs money!).

You can paste the ideas made with Finale Notepad to the full program and even to Sibelius.  
(Version 2006)

ANONYMOUS  This app is more than limited. But it's free.

It is a real drag. But it's free.

It looks more than ugly. But it's free.

It is anything but intuitive. But it's free.

You will go off because it won't do what you intended. But it's free.

It ist useless for any non-beginner. But it's free.

Nuff said?  
(Version 2006)

TOMIS  Would be easier to just notate out stuff in GarageBand2

I know the app is free and all but, who cares if it's not usable.  
(Version 2004)

ANONYMOUS  This program is not a MIDI sequencer

It is a notation utility

the idea behind this software is to put notes on the page. you can play the notes to listen to the score. but you can't export as a sound file (mp3, wav, midi)

this program does what it says it does and for that matter it does it very well. but if you're after a program to create sound files, this program is not for you - get a sequencer instead. but if all you want to do is print out your own sheet music, this program is perfect and i highly recommend it.  
(Version 2004)

STONEBOY  This free version is too crippled to be of any use to musicians. But it is free.  
(Version 2004)

JOEL NELSON  Finale NotePad isn't actually a demo. It is the free version of Finale. When you download Finale NotePad 2004 you will have to register with your email address and have a serial number sent to you, but registration is free.  
(Version 2004)