I've seen far more professional and impressive comparison pics, including some here on Pixalo, but I thought the following two pics still might be interesting. I bought my first fixed focal length (50mm) lens recently and decided to compare it to my zoom lens at the same settings. My friend also has a fixed focal (30mm) but says he doesn't seen any real benefit over his super zoom (18-200mm) so I suggested taking similar comparison pics with his lenses.
Here are the two comparison pics:
Sigma AF 18-50mm f/2.8 DC EX macro Vs. Nikon AF NIKKOR 50mm f/1.4D
Sigma AF 30mm f/1.4 EX HSM DC Vs. Nikkor AF-S 18-200mm f/3.5-5.6 G IF-ED VR II DX
I know most everyone on this board will already know that fixed focal outperform zooms as the same focal length, but if they aren't educational, I hope the above two pics are at least entertaining!