Funny you say this, my friend and i were looking for a really good competitive Keeper league as well. We found one, if you go here: http://baseball.fantasysports.yahoo.com ... ve&ccl=all
Scroll down till you see "3 Sport Dynasty Keeper". You have to "apply" which means emailing the commish and just saying you're interested and check daily, etc. Just click the "apply" button. We're going to keep the same 12 managers for baseball, football and basketball seasons. Details will be emailed to you as well as league id and password if you apply. We currently have 2 spots open, so anyone else that wants to apply please do so! We are all pretty competitive. Once we get 2 more people, we'll go ahead and do a midseason draft for this baseball season.
Normally Yahoo doesnt do keepers, but we have the option to keep the leagues open year-round. We'll just do supplemental drafts the following seasons and the commish will keep track of what team has what players.