What's the absolute best product for routine cleaning of:

1. Polished travertine floor tiles
2. Polished granite counters
3. Honed travertine floor and shower tiles

?

I've found a lot of conflicting information online. Some says to just use water, which seems insufficient to me, especially in the shower, but also in the kitchen. Also a lot of stuff I've found online is about how to do it "cheaply" which isn't really my goal. These materials are a big investment, and I'm happy to spend money to maintain them well. (The stone all came with our house, so we can't ask the installer what he/she recommends.)

We have a cleaning lady, and she'll use any product and tool we ask her to (we supply it), but it does need to be simple enough that she and her helper can do it weekly.

Thanks.