Unfortunately I'm just not sure a great deal for us is there. Monta Ellis isn't going to save this team, and I wouldn't want him as a core piece for the future. Shoring up our bench isn't going to help if our starters are still in and out of the lineup and rarely ever all 100%.
Ray Allen is the only one of the Big 3 who is a real tradeable asset, and it's not clear that we could actually get much real core young talent back for him unless we included Rondo or Perk, which would most likely end up being a lateral move (especially if it involves Rondo).
I think we may have to accept that the KG / Ray trades were a big risk. We're lucky that it paid off in '08, and we shouldn't be that surprised if it doesn't get us any more championships than the one. That doesn't make it a bad trade - this team wasn't going to win a championship anytime soon without that trade. It just means we're probably going to have a few more seasons of being a fringe competitor (ala Detroit Pistons 05-08) and then we'll have to go into rebuilding mode.
Let's just hope the rebuilding process post-Big 3 goes better than the one we went through in the early 90's, or the one Detroit is going through now.