Capacitor and Inductor Filters, no resistor?
The other possibility is that the resistance must come from the rest of the circuit. For example, maybe the input or output impedance of neighboring devices must be considered in series or parallel with the capacitor or inductor to determine the cutoff frequency.


Yes

For instance, see wikipedia second order filter. The load resistor is an essential part of the transfer function. 

LC filters are usually designed between finite resistance on both input and output, but can be designed to have finite resistance on only one port, with a short or open circuit on the other.

The resistance on the port is such an essential part of the design, that if the resistance changes, the filter transfer function changes. When you do finally pick up a book on filter design, you'll see that prototype filters are usually designed for a normalised '1 ohm system', and the final step of filter design is to scale all the components into the actual impedance you're using. 50 ohms and 75 ohms are popular impedances for RF filters, 600 ohms for audio and telephony.