If you are doing this manually, what tools do you use in ArcToolbox?
Based on your title, if you know how to select features within a buffer, then you just need to hit the switch selection button within the table.
The base tools to perform your operations are
Select Layer by Attributes - ie place names, counties, states etc
Select Layer by Location - see this Select By Location graphic examples for cross-geometry examples
You can reverse the selections within the latter.
Now if you need to code this, the code samples in the tool are the way to go. No need for modelbuilder or searchcursors. Use the tools to simplify your workflow, or drag the tools onto a model if you really need to
... sort of retired...