Whenever I travel, I bring $100 in singles and fives for the explicit purpose of tipping because it seems everytime you turn around you have to tip someone. I mean, after parking in the long-term airport parking lot, we tip the parking lot shuttle driver for handling our bags, then the porter at the airport (if we use one), then the car rental shuttle driver when we arrive, then the valet, then the bellman...then I invariably have to tip housekeeping for something that should have been stocked in the room that wasn't (e.g. towels*), then of course, the bartender when I finally pony up to the bar to get my first Painkiller...And that's just on the first day!
As far as TS housekeeping, I usually tip $20 for the week, unless I leave without tidying up or emptying the dishwasher, etc., in which case I'll leave an extra $10. If we bring another couple, the maid also gets whatever they leave.
*I tip $5 for special trips, such as extra towels, but the last few times I've been at TSs, it wasn't because they went above and beyond the call of duty so much as the TS wasn't stocked properly. And I have to say, that I do wonder at the wisdom of doing this, because it rather encourages the staff to not stock the rooms adequately.
For instance, the first time I was at Westin St John, I tipped $5 to the housekeeper who brought up light bulbs... because the bathroom had no working lights at all, a second $5 for maintenance guy to come fix the broken ice maker, then another $5 (twice) for ice to be brought up because the "fixed" ice maker started to leak all over the place.
At WKORV, I paid $5 to 2 separate housekeepers to bring up a working iron, but refused to pay again when on trip #3, when they brought us back the one we returned in Round 1.