There are a few others, which have also done reasonably well, all of
them growing out of doors permanently:

Pelargonium acetosum (Sorrel geranium)- what a fine plant for a
specimen hanging basket. Mine has been out, hanging up exposed to
north easterly winds for several years where it gets watered when I
remember and almost never fertilised. A mass of succulent, very grey-
green scalloped edged leaves and countless large clusters of 8cms.
wide, spidery, coral-salmon flowers throughout summer and autumn. If
it weren't for the fact that it is a martyr to tortrix moth
caterpillar it would be my all time favourite Pelargonium:

http://i10.tinypic.com/6l40bc3.jpg

'Scarlet Unique' is as Peter Sutton infers less vigorous than
'Paton's' and with smaller, less freely produced flowers, but they are
so very flashy that just a few make a lot of impact. It is still
reliable in terms of hardiness here, but can die back slightly in
summer so it is only a moderate sized plant.

http://i1.tinypic.com/6o0brid.jpg

'Captain Starlight' is a 'butterfly Pelargonium' (rather like a regal
but more delicate and smaller in all of its proportions) that has
surprised me by performing well every year. Its slender, wiry, 40cms
high stems are clad in neat, finely toothed rounded leaves and topped
with showy clusters of flower. The upper petals are a velvety
purplish red edged paler, while the lower are mauve lilac with deeper
blotches.

http://i5.tinypic.com/6pje70l.jpg

One Pelargonium was a victim of its own success. Pelargonium cordatum
took little more than 2 years to reach shoulder high and nearly as
much across. I like it because of the very tight clusters of small,
pale mauve flowers carried more or less all at once. The fine
somewhat heart shaped leaves are silvery green beneath adding to the
attraction and it is certainly a very tough shrub. Unfortunately its
largely once-flowering tendency means that it takes up a lot of room
for such a short period of flowering in the year so it had to go.
Pity, because it has a quality look about it.

http://i3.tinypic.com/6ppmia0.jpg