Are you rhetorically asking me to make a list, or are you really asking? Because you pre-emptively posted that regardless of what I post, it won't matter because of the "no one will come here" excuse.
Part of the reason we don't get anyone is because we don't pay top dollar. I don't see much about, "oh, the Spurs offered the same amount, but this prime time guy went elsewhere".
Just to throw out a few though with a quick scan of unresricted free agents:
2008: Diop, Chris Anderson (not much this year)
2009: Zaza Pachulia, Brandon Bass, Chris Anderson (again), Sheed, McDyess (who we got)
2010: Ben Wallace, Shaq, Pryzbilla, Jermaine Oneal, Nazr Mohammed, Tyson Chandler
2011: Turiaf, Pryzbilla, Shaq, Nene, Nazr Mohammed, Tyson Chandler, Dalembert, Fresenko,
2012: Turiaf, Pryzbilla, Jermaine ONeal, Nazr Mohammed, your precious Ian Mahimni, Haywood, Hawes, Fresenko, Camby.
And this year I probably don't need to rehash the guys that were out there. List wasn't huge, but as you can see, a lot of these guys keep resurfacing every year to go play somewhere else for however much they can get.
And those are just centers. I didn't even list any PFs, of which there was a lot more of. I'm not saying we could have gotten each and every one of those guys, but several of them we could have. They were all available if we wanted to make an attempt at them. And again, all I listed was centers, no PFs who don't play C. if I combined that, the list would be a lot bigger.