Ok, so I decided I could come up with a bit of a list, under some criteria - bands where I went out and bought most/all the discography (minimum 4 albums) after being introduced to them by DTF, and I'm still buying their output.
Avantasia
At Vance
Masterplan
Jorn
Evergrey
Royal Hunt
Brazen Abbott
Cloudscape
Primal Fear
Pretty Maids
Pyramaze
Secret Sphere
Vision Divine
Serenity
Axel Rudi Pell
House of Lords
Silent Force
Firewind
Nocturnal Rites
Redemption
Kamelot
Kingcrow
Theocracy
Pagan's Mind
Seventh Wonder
Section A
Threshold
Transatlantic
Frost*
Enchant
Iq
Mystery
Moon Safari
Presto Ballet
Subsignal
At a minimum of 4 albums each, that's minimum 144 albums right there. Some have 8+ that I've bought, and there are easily a couple hundred bands I've got 1-2 albums.