Safari is built-in but I prefer Google Chrome. I don't like Mozilla/Firefox. Chrome by design and real test is the most secure and fastest of the lot. As soon as it gets out of Beta it will be my default browser.
IE8 is a fairly good browser regardless of all the IE/Microsoft bashers. I don't use Mozilla/Firefox at all (it not even loaded). Chrome again is the fastest. I mainly use IE8 because it works so well with RoboForms. As soon as Google works better I will gladly switch.

Internet security is mute in most cases because people use the same password for every website. That why I'm a fan of RoboForms <- Download a Demo Copy good for up to ten websites I have used it for years along with RoboForms togo. AVOID lots of tool-bars!
If you only use 1 computer then you don't need the following stuff but I have 9 computers in my office that I use (5 on a regular bases). So one thing is I need some things on most of the computers so there our several program that help me out ALLOT. The first one is XMarks keeps all computer with the same Bookmarks. Even if you have 2 computers you can get frustrated at not having the links you need. Another program I use all the time is DropBox. Dropbox (free up to 2GB) will make mirror copies of data between many computers, the Internet, and the iPhone or other smartphone. It simple works. I also perfer VLC player (both Mac and PC)
One thing that Apple does is include very good software with all of there computers. iLife Suite is extremely robust and useful. If you need basic spreadsheet and creative word processing along with presentation software then theres iWork. Microsoft Office is the 'standard' Word processor, Spreadsheet Suite. The new kid on the block is Google Doc's it free but totally Web based and that can be a huge problem. Mozy Backup - if you do nothing besides this you. I quit helping people that will not backup there data is quite cheap!
The PC has ten times the software that you can choices. But the worst thing you can do to a PC is load it up with to much stuff! And the issues as to what kind of computer you have like a gaming rig or a Workstation for Video or Picture editing. So the basic thing you will need is First Mozy Backup. Then I for one load the latest Office suite because it always very handy to have. If you got a consumer box then head over to PCdecrappifier.com and download the free program to remove all the trialware that allows Dell to sell cheap computers. The topic of Anti-virus is complicated and will be handled later. I really Like VLC player