There are lots of manufacturers making lots products for floor sealing, have a look at the ranges from the following manufacturers to see if they fit the bill; LTP, HG, Lithofin, there are others.
I'm using a stain stop/sealant product called "Bulletproof" for pale cream marble floor tiles at the moment. I've applied it before grouting and again after.
With limestones/marbles/travertines etc this is important esp. if using dark coloured grouts, as it is possible for the grout colourant to leach into the tile.