INdoors or outdoors? and does it get any sun there?

And how warm is the window sill?

Just as a general idea, if you use herbs then maybe you could grow some that you use on your window sill. Although Bamboo and Moon growe will be able to provide loads more advice :)

I would look into Peperomias, though some species might be happier behind sheer curtains, since there is so much direct sun.

My thought would be cacti

In full sun indoors on a windowsill is a very hot place to be at times - I'd recommend either herbs which you can use for cooking or alternatively, for decorative purposes, succulents such as Aeonium (check out Aeonium aboreum atropurpureum Schwarzkopf), Aloes such as A. humilis, A. variegata, A. mitriformis, Agave (A. victoriae-reginae, A. filifera), Haworthia (H. maragaritiferea, H. fasciata), Sempervivums such as S. tectorum. Or cacti, as Moongrower suggests.
Other more common houseplants generally do not appreciate direct sun, particularly in summer, although you might find something like a New Guinea Impatiens will be fine there if kept well watered.

Fresh basil would be lovely on the kitchen windowsill.....maybe move plants around asthe seasons change

Sadly Pam basil doesn't cope very well with a sunny windowsill - at least that has been my experience...

Slightly odd, since it grows in the full sun in the summer, here in the desert. On the other hand, soft seedlings from some greenhouses may not be adapted for sun. Basil also uses water more quickly than most herbs.

Perhaps it is a different variety that you guys grow Tugb. I have to be very careful of the pot sitting on our kitchen windowsill which faces approx. east. Definitely needs a lot of water, go away for 3 days and it really droops.

Yep, three days would be all it would take, in a pot--usually less, here, due to the low humidity. It's not so much a sun problem, as a watering problem.

Although not suitable for windowsills I find the orchids very easy house guests....they even like my conservatory growing new flowerbuds

I agree Pamg the orchids are easy house guests but not for a south facing window sill as you say.

My conservatory faces north but gets some sun from east & west....and still gets very warm, the orchids are not in direct sun

That is the killer for orchids too much direct sun.

I think that they muxt like it here another one has a new flower stalk

Pamg but you said yourself the orchids do not have direct southern light!

I,ve been wondering about cacti or lithops for this south facing hot windowsill.... I,l never forget my first cactus flowering....magical!