You might consider the Grado SR60 or SR80, both of which can be had for $100 or less. At 32ohms they will be iPod friendly and they are built like tanks. Plus if you don't like them or want to upgrade in the future you can very easily sell them at places like the Head-Fi forum for near to what you paid for them.
I've not heard the Sony MDR-7506 that Adveser recommends, but have read that because they are billed as studio cans they have a sterility to the sound they produce. Most studio headphones are like this and will show most the flaws in your source material. From my understanding they also have a really nasty spike around the 2k region that many can not deal with.
By all means try out as many types as you can if possible. Bring your iPod to the store. Check on Head-Fi.com and see if there is anyone near you that can let you listen to theirs or if a headphone meet is going to be near you. The Sony's may be perfect to you, so please take our opinions as just that. Everyone hears/perceives things differently.