Man, it's hard to come up with a list. I'm not nearly as well-listened as you guys. I'm going through my favourite bands right now, and I don't think any of them has 5 great albums in a row: Megadeth, Tourniquet, Kansas, Vengeance Rising, Dream Theater, Dragonforce, Joe Satriani, Theocracy. As noted above, alot of these bands could make a hellova Hits album, but not 5 in a row!
Megadeath, maybe four: Rust in Peace > Cryptic Writings
Tourniquet, maybe four: Stop the Bleeding > Vanishing Lessons
Dream Theater, maybe 3: Metropolis, Pt. 2 > Train of Thought
I think Theocracy is on its way. Mirror of Souls, As The World Bleeds, and Ghost Ship are incredible. But they're still 2 shy; we'll see what happens in the next few years.
However, I think Skillet has done it in recent years. You could argue that Rise maybe wasn't great, but I've been so impressed with them in recent years. Comatose > Awake > Rise > Unleashed > Victorious. I thought they were gonna crash and burn years ago, but they've just been getting better.