Nepenthes singalana is closely related to N. densiflora and N. diatas. It has the characteristic "toothy" peristome and develops maroonish pitchers. There is a good species profile with adult photos as well in Charles Clarke's book Nepenthes of Sumatra...  My plants have grown at a steady rate similar to N. densiflora and N. diatas. I believe it could be considered an ultra-highlander which would explain its slow growth. This species has been an easy grower for me with no problems. I grow them outdoors in full sun which they seem to appreciate. I don't know the origin of the plant I purchased from Cook's. The "wide form" originated from Borneo Exotics. Most of their offerings for their distributors are size 3 specimens. My largest plant is vining and beginning to put out its first flower spike. I haven't seen any hybrids out their using this species yet either. 

Cultivation: easy; typical slow to moderate growing highlander
Market availability: size 2 to size 3;  somewhat uncommon
Species variability: typical and "wide form" that I'm aware of
$ / size: moderate $30.00 and up
Cuttings: none available for trade
Sex: unknown