Are you set on an IEM? At 150, I'd probably recommend the ER4P if you can deal with the comfort issue and if you like an analytical sound.
Why I asked about the IEM is cause if you stretch the budget a little you can get into the IEM sweetspot, but $150 is not enough IMO. If you can go earbuds, the Yuin PK2 is a great headphone, and it's only 80 bucks and compare favorably with the sub $150 IEM market.
Are you listening to MP3s or lossless files on your iPod? If you have MP3s, spending more than $150 is kind of overkill since the performance would be wasted on compressed music.
The ER-4P are good, but where are you guys finding pairs for $150 or less? Etymotic's 6isolators have a similarly analytical sound and will run $140 at the most. They have low distortion and actually do isolate the listener well.
If you just want a solid pair of IEMs for cheap, consider the Denon AH-C351s. They're $50, have good bass, and low distortion. The only caveat is they have slightly weak mid-range tones, which doesn't particularly lend itself to vocals. For the price, they're a really solid pair of headphones.