I've made it a point to explore everything I could before completing the main quest -- I only have the southern (eastern?) cistern and a couple of safe houses left.

I've completed just about all side quests, I think.

I went into the Lucky 38 and confronted Mr. House. I kept the Platinum Chip. I opened his canister, but didn't kill him. I had previously entered the basemant (via Ceasar's camp) and destryed everything there. I *think* I also used the Platinum Chip to upgrade the Securitrons to Mk. II software (if you can't normally do that, don't ask me how I did it).

Now, when I talk to Yes Man (which I have been avoiding, because I kinda sided with NCR), there's no dialog except for goodbye.

The quest trees don't show me what to do next -- one even show all objectives completed, without the quest itself showing as completed.

Is there someone I should talk to in NCR? How about Ceasar (although I'd rather not -- since I've done virtually everything to oppose him)? Should I go poke around Hoover Dam (oh, yeah, I've kind of avoided there, too).

Anyone have a hint where I should go next?

Have you talked to the NCR ambassador at the southern end of the Strip? If not that's probably where you want to go. He'll have some jobs for you to do and then he'll send you to Hoover Dam (where you'll have plenty to do before the main quest approaches the end).

It looks like NCR is your only option or the legion. Yes Man won't side with you because you destroyed the bunker with the Securitrons thus preventing you from doing the independent path.

Ah, thanks. I forgot all about that dialog that asked me to visit them. That'll be on the list of things to do tomorrow!

That doesn't prevent you from doing the independent path.