If you are looking for scores, well, that's going to take some money to invest.
Are you looking for charts? Go to any sheetmusic store online (sheetmusicplus.com), and you can buy the charts.
If you are looking for notation software, well, if you want the good stuff, that again is going to cost money.
The most popular are
Finale, which has the
Finale Notepad freebie download (warning: Finale Notepad files are practically NEVER compatible with upgraded Finale software).
There is also
Sibelius, which seems to have better reviews than Finale.
I personally use Finale, but I do not object to Sibelius at all.