Even though the original teacher made this project with fourth graders, I know many teachers of middle and high school math who still say fractions are an issue with their students. This is such a clever and creative way to make students work with fractions, equivalencies, and word problems, plus it's adaptable to higher levels if you want to switch some numbers and concepts.
Although eventually students will find surface areas with formulas, the concept of surface area can be tricky, especially while it's still in the conceptual stages. This hands-on lesson really seemed to help, and the manipulatives were very useful for helping explain things to the visual learners. The teacher even said that some of her intervention students, who normally don't give much feedback, said that it made surface area easy. That sounds like a win to me.
This is a blog post that links to a full site, but it has a full selection of some of the more useful math games that teachers can play on the projector for review or have students play during downtime on classroom computers or in the computer lab. The games the blog curated are some of the better ones on the site, but the games on the full site are actual cool math games, rather than unrelated flash games on sites like Cool Math.
This is a full site with videos, teaching guides, and some app links. I probably would shy away from some of the games, although they may be useful to you in some cases, and use the videos. They're decent quality for education videos, they cover good topics, and they're high-interest, so they'd be good for a multimedia lesson. All of the teacher guides explain their standards alignments and are printable, too, which is a massive time-saver.
Many math teachers who teach the coordinate plane have said that they use a game of Battleship to make it understandable. Almost everyone I've spoken to about it says the students love it. This version has a printable template, though I have also seen a simpler version with graph paper glued to cardboard.
Projects often require a lot of money and supplies, but this has a list of class projects and lessons that can be done for free, or at least very cheap. There are lesson ideas for coordinate planes, geometry, probability and statistics, and order of operations here that seem to be very useful with minimal supply costs.
I have to agree with the writer of this project: students LOVE food. I've also seen a different variation of this project with M&Ms, but in general, using multicolored foods to teach ratios is such a great idea. I'd absolutely use this to motivate students to learn math.
This is another site that is just a list of sites, but it really breaks down a bunch of websites that math teachers have found invaluable in their teaching. There are links to everything from virtual manipulatives, graphing, calculating, and inquiry-based lessons. I say this on a lot of sites that list sites: I am so grateful to see people who share their useful sites so that teachers don't have to spend time on sites that don't work or don't help.