vNES
Note: This article was published while I was in my early 20s. I was much younger and dumber. Please don't hold it against me. One of the perils of having a 20+ year old website!
While scanning the internet the other day (something I tend to do every 3 hours or so), I came across a nice little site called vNES. It is an NES emulator that runs right from the browser! It uses Java, so you will need that to use it, but that is a small price to pay for this. Select from a number of classics including 1942, Super Mario Bros., and my personal favorite, BattleToads. They are currently working on saving games and mapping your own controls, among other things! It is definitely a site to check out. Later!