What is this an example of: "FOR SALE: Car by elderly lady with new body and spare tire"

Historical examples:

• Croesus asked the oracle what would happen if he attacked Persia. The reply: ‘A mighty empire will be humbled’.

• Thank you so much for the book. I shall lose no time in reading it.

Modern example:

I am opposed to taxes which slow economic growth.

Humorous:

The anthropologists went to a remote area and took photographs of some native women, but they weren't developed.

What is the term used for these examples?

These are examples of amphibology. To quote its Wikipedia entry:

Amphibology or amphiboly (from the Greek ἀμφιβολία, amphibolia) is an ambiguous grammatical structure in a sentence.

These are examples of syntactic ambiguity. They demonstrate ambiguity between alternate syntactic structures underlying a sentence.

• The man saw the boy with the binoculars.
• They are hunting dogs.
• Free whales.
• Police help dog bite victim.
• He saw that gas can explode.
• We saw her duck.
• The kiwi eats roots and leaves.

See http://en.wikipedia.org/wiki/List_of_linguistic_example_sentences for this and other types of lexical ambiguity.

This is a classic example of a misplaced modifier.

The sentence in your title contains a classical figure of speech commonly called zeugma (your other sentences are rather double entendre or simply ambiguous, as the others have mentioned). See Wikipedia on zeugma and syllepsis; what Wikipedia calls syllepsis is usually simply called zeugma, as syllepsis is the most common significant application of zeugma in rhetoric and literature.

Zeugma (from the Greek: ζεῦγμα, zeûgma, meaning "yoke") is a figure of speech describing the joining of two or more parts of a sentence with a single common verb or noun. A zeugma employs both ellipsis, the omission of words which are easily understood, and parallelism, the balance of several words or phrases. The result is a series of similar phrases joined or yoked together by a common and implied noun or verb.

...

Syllepsis, also known as semantic zeugma, is a particular type of zeugma in which the clauses disagree in either meaning or grammar. The governing word may change meaning with respect to the other words it modifies. This creates a semantic incongruity that is often humorous. Alternatively, a syllepsis may contain a governing word or phrase that does not agree grammatically with one or more of its distributed terms. This is an intentional construction in which rules of grammar are bent for stylistic effect.

See my answer to a similar question here: Books and other things with the same name .