Disclaimer: I do not condone or endorse using your time on the clock to aimlessly surf the internet…actually I don't care what you do at work but if you get caught it's your fault, not mine. I bear no responsibility.
One thing the internet has allowed us to do is spend time doing something besides the thing we're supposed to be doing. Why work on that TPS report when you can watch a cat leap into a mirror? Of course, work does need to come first, but sometimes you just need a few minutes to browse and give your brain a chance to relax. As long as you can get yourself to get back to work, there is nothing wrong with doing a little web surfing on the side.
Sadly, checking your email doesn't do the trick. You need more, well wait no longer because I've got a good list of sites to peruse when you need something to lighten up your day.
The first is Livejournal. It's a blogging site, but it can get rather addictive. You'll just login to check for updates only to find that someone posts a new entry or comment just as you log out, which in turn makes you want to log back in to see what you missed. It also gives you a place to vent if you're having a bad day.
There are of course the other "social networking sites" like Facebook and MySpace. They aren't as good as LJ as there is only so much you can do with these two sites, still they are pages that you can check on a regular basis to check for updates.
Another site is Ctrl Alt Del. This is a webcomic that is updated three times a week. If you're a gamer, than this is definitely worth checking out.
Another great webcomic is the Dinosaur comics found at Qwantz.com. Updated daily, this uses the same six panels only with different dialogue. There are a lot of "back issues" so if you do decide to check this out, keep that in mind as it took me several months to go through them all.
Like cute animals? Check out Icanhascheezburger.com there you will find things known as "lolcats". They are essentially pictures of animals with funny expressions or in odd poses with an amusing caption. The beauty of this site is that it links to a bunch of other spin off sites. After the lolcats, you can check out loldogs, lolcelebrities, lolpoliticians, and lolepicfails. It gives you a good break without being too time consuming.
The final website I submit for your approval is thatguywiththeglasses.com. I discovered this site recently but have been highly amused by the videos. From Nostalgia Critic to the Bum Reviews, these videos have often left me unable to breathe as I was laughing so hard. Some of these videos are rather long comparitively so this one might need to wait until you get home, but it is definitely worth checking out.
As long as wandering these websites doesn't consume your entire workday. I suggest browsing them occasionally when you're feeling stressed. Relaxation leads to better productivity and that will make you a better employee. Before you burn yourself out and raise your blood pressure even higher, just take a deep breath and spend a few minutes looking at all the amusing and entertaining things the internet has to offer.