For me it's either a $100 pair of Shure or Etymotic, or a $10 set of Sonys. Sony has been making the same $10 pair since the early '90s, and I have no problem buying another set; they usually last me a couple of years, but sometimes I lose them or they get destroyed somehow.
Looks like my current pair is currently $4.25 on Amazon:
http://www.amazon.com/Sony-MDR-E828L.../dp/B00008VF63
In the realm of low-priced earbuds, IMO, ear-fit is actually more important than sound. In this regard I have never found a need to change from the El Cheapo Sonys. They fit my ears very well, and they don't have any sharp edges or other uncomfortable bits. I need buds that will stay in my ears while jogging without falling out, and that I can wear for 3-4 hours without fatigue. The Sonys work for me in that regard, but everybody's ears are different shapes and sizes. I started using the Sonys back in junior high, and they haven't changed them much since then other than minor cosmetic changes.
About a year ago I got a pair of the JVC "Marshmallow" buds for about $20 from an airport vending machine when I forgot my Sonys at home, and I was pretty happy with them based on their noise-abating properties (I even used them as earplugs in noisy environments) but unfortunately left them on a plane somewhere.