Census data is useful since state and federal censuses often contain additional demographic data, such as vital statistics (births, deaths, marriages), as well as state or country of origin, which can aid in immigration studies. When using census data it is generally accepted practice to utilize a single generational component, usually the heads of households only.
Another source of data are town directories. Throughout the 19th century, directories of town residents were often produced, though somewhat irregularly. These directories essentially functioned like phonebooks without the phone number, giving the name of the head of household and address. Directories have the advantage of being typed records, rather than handwritten census records. With the advent of the telephone, naturally the phonebook took the place of directories. Phonebooks have been used extensively in isonymy studies, particularly when the information is available via CD-ROM.
Beyond the three major sources listed above, data sources are only limited to the creativity of the researcher. Indeed, any specific record of individuals may represent a biological sample of some population. For example, Gabriel Lasker utilized militia roles from the Revolutionary War as random samples of males from bounded populations. Another possible source of data are cemeteries. Many cemeteries include grave markers listing married couples, which would constitute a source of marital isonymy data.
One of the most significant developments for surname research is the fact that many of these data sources are now becoming available online. Historical societies and genealogical websites are beginning to transcribe census and historical directory data on to the internet. Of course, you are taking a risk of sorts when utilizing transcribed data alone since you are relying on the accuracy of the transcriber. This may be especially problematic when the information was originally hand-written. Then again, much of this work is being done by dedicated volunteers, who can be quite adept at both translating hand-writing and identifying alternate spellings of words. When in doubt, check out the hard copies yourself at the county offices or local historical society.