The subject we get asked the most questions about is definitely Math. Let me share what we'e using for Math curriculum at the moment:
C16 is continuing down the Math-U-See path with great results. Every once in a while I show him another curriculum that friends are excied about (like Khan Academy or Teaching Textbooks), but he is content with this program by Steve Demme. This is his fourth year of using Mth-U-See; four years ago we started with Gamma (typically a 3rd grade level) and he quickly got caught up to his same-age peers. He's on the 23rd chapter now. When he completes this level, he'll take a pause before beginning Algebra II or Geometry, and probably will join his twin in some math games.
The only trouble with Math-U-See is that we don't take a DVD player with us on the road, so when traveling I take the Teacher's Guide book.
N16 had started Math-U-See Pre-Algebra, but I just got too frustrated guiding him through problems with so many steps (ones where you use all sorts of operations and he often got mixed up). I still am a fan of Math-U-See Pre-Algebra, so I thought that maybe after another year of maturing and mastering basic math concepts he could try it again. If it doesn't work for us when I make a second attempt in the fall, we'll come up with a new plan for math.
For now, we have tackled many mathematical critical thinking skills, money math and have enjoyed activities from the book MathART. He also does some drill work and word problems in a workbook. He's still doing about 30-60 minutes a day of math activities, but he just won't earn a Pre-Algebra credit this year.
Little A3 is currently working on patterning, which is fun for all of us. When he's using edible manipulatives (M&Ms, gumdrops from Trader Joes, etc), his big brothers usually find an excuse to join him. I have to hold myself back from buying every adorable manipulative set I see, but we do enjoy Let's Tackle Math and a set of Pattern Beads that I ordered from Amazon. Patterns are easy to teach and practice, but I have loosely followed Count on Math for him so far and plan to continue through the end of the book. He knows his numbers 1-20 and finds many opportunities to count throughout each day.