The thing is, if you fall in love with the band, you'll end up owning them all anyway. If you like more modern sounding stuff with flawless production (so flawless, that its a little cold in my opinion, but still a technical masterpiece), get Dead Heart in a Dead World. Its probably the most accessable album from a new prospective fan's standpoint. Then try working backwards.
If you like more brutal thrashy, hateful, emotion filled metal, try Dreaming Neon Black or Politics of Ecstacy. Their first album is good, but it reminds me of a heavier Sanctuary, and Sanctuary IN MY OPINION is a really aquired taste. Some of that stuff was REALLY cheesy, if you're down with Priest then its cool, but if you want a more accurate representation of what Nevermore is about, then get their first record later. Its still good, just not what they're doing anymore.