The two biggies are Finale and Sibelius. I couldn't afford Sibelius, so I went with Finale. The great thing about it is they have a free version, a $50 version, a $100 version, a $200 and the "real" $600 version. Any version can load files from the other versions, but can't edit the "advanced" features. They also to a 30 day demo on most versions...
I downloaded the free version, and found it overly crippled (no key changes, limited repeats, bass tab is buggy: hey it's free - don't knock it), so I downloaded the 30 day trial of the $50 version - OK but couldn't do double bars and a couple of other silly things, so I got the trail version of the $100 version (printmusic). I used that for a few weeks, and while it has a few bugs, it supported everything I needed, and I got the job I needed done. When the trial expired I was still able to make some minor fixes using the free (notepad) version.
The next time I needed it I dropped the $100 and payed for it, so now I have printmusic on my main machine, and the free version on a couple of other machines, so I can view/tweak files on them too. If you ever decide you need a better version you get to upgrade for the price difference (in fact if you register notepad you get $10 off the commercial versions).
It is buggy, and quirky but the results look great, and they make it very easy to buy, allowing you to trail and mix versions. Sibelius might be great but it's $1000, so it's not even in the game for me.
Ian