Substances comprised of large molecules are liquids at room temperature?
You may give porphyrins a try.  These dyes are of interest for molecular electronics, and to render them less crystalline / more glassy, alkyl chains are attached to the central motif.  One recent example are the room temperature liquid porphyrins developed in the group around professor Gryko:

(source, Chem Asian J. 2010, 5, 904-909; doi: 10.1002/asia.200900693.)
Besides standard spectroscopic characterisation, the publication contains the results of DSC:

so compound 4d ($\ce{C176H294N4O12}$) may be a good candidate for an organic molecule, without charges and metal coordination, and suitable for ellipsometry / VASE measurments on surfaces.