Combo! and Blockdown are two great Flash puzzle games by Anders Pousette. They're remarkably simple and build upon classic puzzle gaming themes while throwing a few fresh ideas into the mix. Each comes with a public high score board to give you a chance at your 15 minutes of fame. You'll have to earn it, but with the amount of time you'll spend playing each game, odds are you won't really mind.
Combo! supplies a field of blocks flying in four directions at many different speeds. Using your spinning square of doom (ok, I made up the name), you must collect as many colored blocks as you can while avoiding the splotchy black blobs. To make things a little more interesting, a combo pattern appears at the bottom of the screen showing you a series of three colors. Capture squares in that order to get a score multiplier. The more you capture, the bigger the multiplier. If you collect a square that doesn't fit the combo your multiplication streak ends. On top of that, the combos are timed and change every once in a while, so you have to keep your eye on the timer. Combo! pulls your attention into several different places at once but manages to keep you hooked. It seems like it should be frustrating, but it's incredibly addictive.
Blockdown is a variation on the falling-blocks theme and plays like a cross between Breakout and Tetris. Except... upside-down. You control a small rectangle at the base of the screen and must catch falling blocks and stack them neatly at the bottom. Line up three like-colored rectangles to make them vanish, but don't let them stack too high. You can hold large piles of bricks and set them down wherever you need, but it's a challenge to balance block catching with block dropping while dealing with the odd brick that falls without you realizing it. It can get pretty frantic after a few minutes, but it won't let go of your attention for quite a while.
While both games are simple in terms of gameplay and graphics, one area I would love to see fleshed out a bit is the sound effects department. Combo! and Blockdown are completely silent, free of bleeps, bloops or background music. It's an interesting change of pace (and certainly preferrable to an annoying soundtrack), but I feel that even a little sound here and there would enhance gameplay. Blocks could make a "tink" sound when landing in Blockdown and gathered squares in Combo! could say, for example, "schwoop". Their exclusion doesn't detract from the experience of course, but a noise here and there might be a great addition to the already entertaining games.