ITR, how many sq ft is your travertine deck/walk areas? Is you coping travertine too?
We have over 1200 sq ft of travertine re decking, walkways, sun-decks and summer kitchen area. We have all travertine coping, top of spa, column heads and walls. The columns are also all travertine for scuppers and fire bowls, so we have a lot of different shapes, patterns and layouts, but they are all a neutral color so it all matches.
SuzfromTX, I used Aquamix Enrich'n Seal for the coping and the travertine that is one the face of our kitchen This "shades" the travertine some and pulls out all the diff colors, kind of like when it's wet from a nice rain. It really depends on what type of travertine you have. Also, if you power-wash, do not use anything above 600-880PSI...strong PSI's can blow-out a lot of the finer sediments in the travertine and leave your stones pitted. These pits collect water, dirt, debris, etc and can promote molding. Also, if your Travertine has iron in it, it will rust and turn orangish-brownish-red. You can hit this w an anti-ferrous oxidizing agent that will neutralize the rust, then you can brush off and seal. It's the comb of water, sun and the ferrous in the stone that rusts. the sealing agent prevents moisture penetration and thus no rusting. You can hit these areas twice, but make sure you follow the directions for all timelines.
I used the Dupont StoneTech on all of the pool line travertine, the columns and wall and the spa spillover before the pool was plastered/pebblesheen'ed. Its a good sealer, but the Aqua mix product seems to work a lot better, that is for tumbled travertine that we have. AquaMix is not cheap, but your biggest cost is labor. It takes almost the same labor so you might want to go w the one that lasts the longest. Also, many good quality sealers will require that you wipe it down 20-30 min's after application. if you have someone doing yours, make sure they do this or ask them this up front. If you do not do this, it can later look wet like clear syrup is on it, and it will wear differently and make your stones look irregular in appearance. Just have the installer following the instructions.
Good luck,
tstex