Like Warwickhunt said, there's a massive conversation about this already in existence. Only thing I would say is don't try and save money on cheap IEMs. Finding a decent set with good bass response was a massive toil for me. Eventually paid around 900 quid for a set of in ear moulds and 6 drivers per ear. If you think about the combined processing power (and money) of your bands mics, preamps, modellers, etc, why are we all then surprised when it doesn't sound good through our 90 quid set of headphones?
(Saying that I bought a pair of KZs as a back up for around 35 quid and they were surprisingly good. As good as my 900 quid pair? No, but my moulded ones aren't worth an extra 850. Ah well you live and learn).