I took a punt on an iBasso D-Zero MK2 (~£90) a while ago and have been pleasantly surprised. It's a DAC/Amp that works with Phones/Windows etc. It is a significant improvement over standard laptop/phone output.
Just remember, the headphones/speakers you use are the most important part of the sound you get, then have a look at the source. I think a general rule of thumb is if you spend £100 on headphones, you might want to look at spending a similar amount on the DAC/Amp driving them.
What are you currently using for headphones/speakers and source?