Qwyzzle is a big brainteaser. It's pretty addictive if you are into this sort of thing, but getting it to work properly can be a challenge. Many hints are provided in the status bar, but recent versions of Firefox and IE seem to have some problems with them. Today, I had more success with IE than with Firefox. I completed it a couple years ago. I recall that I went to help sites a couple times, but was able to do most of it on my own (I used Google a fair amount, but avoided cheat sites.)
not pr0n seems to be a geek's brainteaser. It took me a while to get through level 2, but levels 3 through 6 were much easier. I have really only started this, but it looks like good fun. To give you an idea about the addictive nature of not pr0n, I have had to edit the preceding sentence three times in the past half hour. It started as "3 and 4", then was "3 through 5" and finally the version you see. Now I have to force myself to go to bed. Work to do tomorrow.
Note that unlike samorost (which I blogged a few days ago), these brainteasers are easy to pause. Just bookmark the last page you get to and you can jump right in at that point any time you want.
If you are still reading this, then you are probably at least a little bit of a geek. Here is a video about a really special set called the Mandelbrot set. I know that a video about a set sounds like a pretty boring idea, but this video is pretty nifty. The Mandelbrot set is...well...er...um.... Forget it. I won't bother trying to explain it since this video does a far better job than I could ever do. Be sure to listen to the lyrics.