I do tip the cleaning staff. I leave $5-$10 in an envelope (which I have to bring with me) and write "HOUSEKEEPING" on it.

Of course, most rental places expect you to leave the place really clean, and we do, but still, maids make lousy money, it's hard work, and I assume they appreciate it.

For the owners, I write in their guest book (most provide one) how much I enjoyed my stay and how pleased I was at how well-stocked the place was.

If and only if the place is the primary residence of the owner, rather than a rental-only place, sometimes I'll wait several months and write a little thank-you note telling them I was among their summer renters and how very much at-home I felt. Twice now the next year's slightly increased rental rate on the same house mysteriously dropped to the previous year's level when they sent the contract–presumably at the owner's request. Nice works!