Correlation between functional group and viscosity of an organic compound?
There are empirical methods that can give you the viscosity from the structure. For lower temperatures, Orrick-Erbar equation, and for higher temperatures, Letsou-Stiel equation is what you are looking for. Orrick-Erbar maybe more suitable for you, because it is a group contribution method, and by looking at the values assigned to functional groups, you can develop an intuition about how each group affects viscosity. Letsou-Stiel uses acentricity factor, because at high temperatures, secondary bonds become less important.

As for database, NIST may be useful. Or if not, look at some supplier webpage (I use SigmaAldrich for this).