I agree with 'cleaning', all these are good ways of increasing revenue - alot at higher margins than the actual cleaning itself.
A word of caution about re-lamping. If you do go down this route ensure that it is carried out by a suitably qualified electrician (a team of 2 if working at height).
I remember a claim against Toys r Us where a manager had instructed an unqualified member of staff to change some lamps. He suffered an electric shock. Toys r Us were heavily fined. They now use a specialist company to carry out this work.
Others to add to your list could include dust mats and roller towels, laundering of tea towels and hand towels, stripping and sealing hard floors, high level cleans etc.
We even supply a couple of bunches of flowers to one of our clients on a weekly basis.
Musicman