I think you'd really enjoy Queensryche's Operation Mindcrime if you like Maiden. (My official Cheese Detector does, however, report a "moderate" level of cheese, for almost anything Queensryche does)
Also, check out Gamma Ray's No World Order. Its more power-metal-ish, but it definitely fell from the Maiden tree, and didn't land very far from the roots
(Cheese factor - "medium-high") (EDIT: hmm.. I just listened to it again, and I have to say it fell a bit further from the Maiden tree than I originally anticipated.. still, its really not bad)
Personally I love In Flames, and would second the reccommendation any day, but since you want semi-intelligible lyrics, you might not enjoy the aorta-rupturing death-metal screaming that In Flames is famous for
If you care to risk it with something a bit out there in the left field, check out Divercia's Modus Operandi. I am really not sure where to classify this. It has a power-metal feel to it, but... its got something else too. Anyway, their music is quite different from what I expected, in a good way. (Cheese detector is not picking up a signal.. is it just me or are these guys really serious?)
EDIT#2: Oh yea, check out some earlier Fates Warning, like The Spectre Within.