Hi sonicfox,
At an amazing budget level, look for the Koss "The Plug". They are about $15 and if they comfortably fit your ear canals (that's a big IF with all such earbuds), you'll get amazing bass, some sound isolation, and quite neutral and detailed mids and treble, though not quite as detailed as the M2s, M22s, M60s and M80s.
But I much preferred them to the disappointing $139 Etymotic Research earbuds, which had little bass, and an overly sibilant midrange peak. Plus I found the Etymotics uncomfortable even after trying different sizes of tips.
The ear canal fit is crucial, in my experience. Whatever you try, get a selection of different-sized tips. Even the cheapo Koss Plug comes with a variety of different tips.
Regards,
