There have been a series of game design articles on the blog Square Fireballs recently, specifically offering some houserules for D&D 4E. Most recent was a compilation "playtest package" summarizing the first round of changes. They're definitely worth a look if you play 4E, as they address some issues with the system and offer solutions based on sound logic and play experience.
They're not perfect (not surprising this being the first draft and all), but they definitely have me intrigued. I particularly like the idea behind Action Point checks, and the new Dying and Healing Surge rules. I'd encourage anyone interested in making some "tweaks" to their game try some of these rules out; you can always not use them if you don't like them, and your experience might even help them get refined.