Dendrobium teretifolium (the "bridal veil" or "pencil" orchid) The individual flowers aren't pendant, but the whole plant is - and is capable of blooming a couple of times a year, a big specimen can be in bloom all summer. Also Epidendrum parkinsonianum - again, it is the whole plant that is pendant. A specimen-sized plant in bloom is spectacular, and even in when not in bloom, quite attractive.
if cascading bloom display is your thing, you could try to grow dendrobium anosmum or den. aphyllum. they both are capable of fantastic bloom displays and are easy to grow. another plus to growing them is that the blooms are fragrant.
We are just entering the cymbidium season here in the UK so you are looking for cascading cyms at the right time. Take a look at Burnham Nurseries web site or give them a call as they normally have a few nice ones. They are based in Newton Abbot, Devon and travel to orchid shows all over the country.