What are the best Sennheiser headphones for listening to an ipod?

I enjoy listening to music and watching DVDs on my computer pretty frequently, I also enjoy listening to music on my Ipod. I've been doing a bit of research but would like some extra input as to what may be the best headphones for an Ipod for around $100-$150. Similarly, would an amplifier greatly help? If so, what would be a good product?