If for some reason you don't know what Firefox is, like you've been living under a rock, it's an excellent alternative to Internet Explorer. It's also the Default web browser in Ubuntu. There are a few minor differences between the Firefox in Windows, that you may be used to, and the Firefox in Ubuntu.
The first thing you may notice is that Tools > Options is not there. Instead look in Edit > Preferences.

I must admit, Microsoft Office is nice, but Open Office does everything I need to do.

What about Photoshop? Gimp (GNU Image Manipulation Program) is another great open-source alternative that exists in Windows and Linux.

Got AIM, Yahoo, Google chat? It doesn't matter, use all 3. Empathy is a messaging program which supports text, voice, and video chat and file transfers over many different protocols. You can have all of your buddies in one list. It even gives you the ability to chat to other Empathy users on the LAN.

With Compiz, Ubuntu's OpenGL window and compositing manager, your desktop can do some pretty cool things, like wobbly windows, desktop cube, & exploding windows!

If for some reason you feel you have to use a Windows app, try Wine first.