Lots of sources
I use my iPod nano for travel and for drumming but my main stereo exposes the compression (even thought the Firewire Audiophile) so I still buy CDs for their clarity.
I found Nightwish from Youtube, went out and bought their CDs. They really remind me a little of Iron Maiden (infact one of their songs ends with an ending blatently stolen/influenced from The Trooper).
I just love the tunes that blaze along with Tarja's vocals soaring over them such as Stargazers, etc. Their drummer's rather good too with very good scores, later that's not the case with the new vocalist

Can't beat End of All Hope though.. it has become one of my favourites of all time.
I just put in female metal into Youtube and ended up with a gem!
I found Guano Apes ages after their time, initially from the video of the japanese troop doing lots of crazy stuff to the sound of Open Your Eyes. Which I kept playing again and again because at the point in time it just hit the spot tune wise. My female flatmate (new at that time) was playing Helloween (she's very reserved proper lady but loves good -cheesy- rock!) identified it as a tune she had ... I bought the CDs after that too..
I found Aghora from a thread on OcUK, I found them on iTunes and liked the sound so they're on my iPod.. I've also suggested them to the guys on the Vdrums forum because if the interesting drum scores. The drummer does make mistakes but I assume they're short of recording time but the interesting nature makes up for it.
Buddy Rich .. from a movie score. I remember hearing this and attempting to find it before but without success. From the credits I worked through them to find it.. then I found it was also one of the best drummers so that's opened my eyes.
Red Snapper - quite often I'll just buy a 5 CDs or nowdays iTunes or perhaps look on youtube.. I've seen RS live and I went shopping one day and I popped into an independent record store and their album was there. Bought it on the spot.