The Savage Species and Players Guide to Faerune both have excellent ways of implementing ECL's. Another way that i have seen (don't remember what resource I picked it up from, perhaps Dungeon Magazine) is to allow the player to create the +1 or greater ECL character and penalize their d20 rolls (all of them) by the total of their HD and Level Adjustment. Let them earn exp just like everyone else (starting at 0 and going to 1000, then to 3000 etc.). When then gain a level, deduct one point from their penalties until they are at zero penalties. Then they are even level with their ECL and can gain class levels. I have tried this a few times and it seems to go pretty smoothly. I had a player create a Half-Red-Dragon-Treant (sounds wierd, but we had story reasons for it) which put him at a -5 or -6 penalty to his d20 rolls. We played through 8th level from 1st level and the character didnt hog the spotlight or overpower the encounters. Try it out a few times, you'll be glad you did.