We adore Singapore Math! The focus on "mental" math and heuristics instead of learning some "one right way" to get the answer is great for GT kids, I think. I agree that it's a wonderful value for the (very little) money. Get the "Intensive Practice" workbooks instead of the regular ones, though. They're much better than the regular ones at "deeper, not just faster," even for basic arithmetic, I think.

Singapore is the only math we've tried, though, so I wouldn't say I'm an expert by any means...

Kriston