I am a Bass-Head.  I had a pair of Sony on-ear monitors, and they were uncomfortable and didn't sound good, so I decided that it was time to buy new ones.  I did some research and decided that I wanted a pair of over/around-ear headphones with thumping bass for under $100.  I researched Beats, Bose, Sony, Skullcandy, JVC, Koss, Panasonic, and finally Sennheiser.  I decided to go with the HD 419.  I found them for $35 from B&H and bought them.  They came the same week (with free shipping).  I opened the box, put them on, and plugged them into my iMac and iPod touch (no external amp used for either).  This is my review:
 
Design:
These headphones look and feel AMAZING!!  They are very comfortable and light-weight on your head.  The only complaint is the thin cable.
 
Isolation:
When I put on the headphones, I couldn't hear much noise from my surroundings (with no music playing)!  I turned the volume almost all the way down, played some music, and I couldn't hear ANYTHING other than my music!  They also do a good job at keeping music in, unless you have them at high volumes.
 
Sound:
These headphones sound AMAZING!!!  The bass is perfect: clean, un-distorted, and punchy!  Highs and mids are great too, but these are DEFINITELY bass-centered headphones.  They can also go VERY loud.
 
Power:
All my tests were done on a 2008 iMac and an iPod touch 5g, with no external amp used.  However, on the iPod, It seemed like the sound won't go as loud, so if you intend to use with an iPod/iPhone, you might want to get a cheap headphone amp.
 
Verdict:
These are VERY good headphones for people who want LOTS of bass for a budget price.