Another manga I've recently learned about is called "Elite Yankee Saburo." It's not an ecchi manga, but there was a live action version on Japanese TV a while back that worked some ecchi content into each episode. It's a story about a normal straight-arrow boy that enters a kind of Go Nagai-type high school that's apparently run by gangs. His 2 older brothers were the bosses and apparently his entire home room wants to join his gang and take over the school (and he just wants them to act normal and go away.) Meanwhile the other rival are out looking for an opening - one is a gang of three girls called the "Stupid Peach Princess gang" that shows up in every episode, usually with their tops off or stripped down to their panties. Some Dailymotion clips:
http://www.dailymotion.com/video/x1z...yyyyyyy-1_sexy
http://www.dailymotion.com/video/x1z...yyyyyyy-2_sexy
http://www.dailymotion.com/video/x1z...yyyyyyy-3_sexy
http://www.dailymotion.com/video/x1z...yyyyyyy-4_sexy
http://www.dailymotion.com/video/x1z...yyyyyyy-5_sexy
http://www.dailymotion.com/video/x1z...yyyyyyy-5_sexy
Here's some stills: