Welcome to the world of Linux. If you want a good software for updates use up2date or yum, they'll most probably already be on your system. If you need new packages, yum will usually also do the trick. There's a graphical interface for it called yumex which gives you package lists to choose from. You can also extend the package list by installing new repositories. If you need software sources, go to sourceforge
, you'll find practically anything there. Hope this helps.
EDIT: Google is also your friend. Search for any utility and you'll find it there.