New to headphones - what amp, source?

I just purchased some headphones (Sennheiser HD650) and I haven't had headphones for over 25 years, since back when you could jack them directly into your receiver. If I want a relatively portable set up, I could use an amp like the Ray Samuels Hornet (other suggestions?), but what are folks using for their source that isn't too big? Do most use a full sized CD player, or are there portables with rca outs? I am not really sure how to set this up, so any help would be appreciated.
I am using an Imod'd 60gb 4th generation Ipod I bought from Redwine Audio for $425 with shipping and will probably buy mini-to-mini cables from Audiolineout to connect the ipod to my portable amp.
There are plenty of portable CDPs with RCA outs, including one rat shack unit (forget the model #, should be able to google it) that was supposed to be a real giant killer. If you want something relatively portable, that is what I would get with one of the Ray Samuels portable HP amps. For characteristics of the all the various portables, try
Ray Samuels makes excellent headphone amps and his portables are great. However, for portable use, I use an 80GB i-Pod with Apple lossless and Etymotic ER-4P in ear earphones and no portable amp. This gives me great sound and great portability. I have owned 2 very good portable amps that I used with an i-River H140 MP3 player and I must say that it was a pain to have to carry a portable amp around. If you still want to get a portable amp, the Hornet is a good way to go. If you use an i-Pod and a portable amp, the best way to connect them is to use a line dock out adapter with a mini plug because it bypasses the i-Pod internal amp. A home amp rather than portable amp will give you the best sound with your 650's. For portable sources, an 80GB or 30GB i-Pod is a great and very user friendly way to go.
Smatsui gives v. good advice.