Nuke Anything
R.I.P. (Remove It Permanently)

These two both perform about the same function. Very easy and convenient to use, just right click on an object in a web page and in the right click menu, click on "remove this object" or something like that, and it's removed from the page. Great for removing banner ads, except doesn't work on flash =\. Also I use it to remove pictures or other objects msnbc likes to place in their news stories which get in the way of the text a little bit. I've used NukeAnything for a while but only now just trying out RIP, so don't know which is better. RIP seems to be a bit more advanced though *shrug.

Aardvark
The same functionality as above extensions but WAY more powerful. The trade off is that you have to start it first. That is, you right click and in the right click menu click "start aardvark", only then can you use its removal features, and at the end you have to close it again. But when you have it going, it highlights each object you're mousing over with a bright red box so you can see and select very precisely the frame/object you want to remove.


Flashblock
Blocks all flash. But each flash object can still be clicked to be downloaded and played/displayed.


Sorry if any of these have been mentioned already.