If your ipod/iphone music is at top volume but still not as loud as you like, try placing it in a glass cup. (I won't go through the scientific explanation, google will help you with that.) This is a simple but effective/weird trick.

Tips: Sounds vary from cup to cup, depending on the height and material. Works best if the cup is taller than the ipod/phone.
Warning: Make sure there is no water in the cup first. (This should be obvious, but I need to say this for some of you morons out there.)

Google