If you're into vintage audio, and don't need to carry your headphones amp around, then Crown D-75 makes a really nice headphones amplifier, especially if you're using high impedance headphones.

Too bad obobskivich isn't around anymore --he is definitely the one to ask when you need advices about headphones.

I've been using a FiiO Alpen E17 for about 9 years now and it produces wonderful sound. It's a DAC (portable, smaller than an ipod classic) and has completely removed the need for me to have a sound card. These days its with my laptop all the time when working either at home or in the office.

I use it with Wharfedale isodynamics which have 120 Ohm impedance (and are recommended to plug directly into speaker terminals due to the power they require) but it drives them absolutely fine.
The screen has burnt in, which can be avoided by switching to hold... I just never remembered to do that 😒, but that is my only complaint (although some say the battery can drain when not used for long periods of time, but since mine is plugged into my computer, and my computer is on every day, I have not noticed this). Would recommend it anytime. Portable easy, plug n play, no sound card required, works in WinXP.

The price seems to have dropped by only 10 pounds after all these years.