Adblock--permanently remove any ads or images you don't want to see.
miniT--adds drag and drop to tabbed browsing
BBC code--adds a context menu to make formatting of your posts more convenient.
Don't use any huge tab browser extension with lots and lots of features. There has been a buggy history with such extensions.
Play with customizing your toolbar by right clicking an empty area on the top menu bar and selecting "customize" from the context menu which appears.
A couple of security/privacy settings which I suggest:
Go to tools>options>privacy>cookies. Check allow sites to set cookies, and "ask me every time" where it says "keep cookies."
Go to tools>options>web features. Remove a checkmark from the box that reads, "Allow sites to install software." When you want software downloaded,check the box, and uncheck it when you are done.
Take a look at Thunderbird for your email client if you happen to be using Outlook or Outlook Express.
