The previous answers are not quite right, but it's a very tricky question.

The third example, "to get out of debt" is a bit of an exception. One reason to use 'get' instead of 'getting' here is because get makes a nice rhyme with debt, for the purpose of selling books. So I wouldn't use that one as an example of typical usage.

I think the default is actually 'getting' instead of 'get.'

However, it seems that 'getting' would feel unnatural in the last example. I think the issue here is that the 'get' in that example is used in a more complex way, where the real verb is not 'get,' but "get started", and "get started" has a double complement. Who got started? you. What did you get started doing? making money. This is not true of the other examples.

To Get is the normal form and would be best for everyday use. However book titles are allowed artistic license.

Regarding the to Getting forms, I would think of it this way:

1) The Essential Guide to (doing something) + (which is) Getting Your Book Published

and

2) The Guide to (doing something) + (which is) Getting it On

In these examples each phrase can stand on its own, but you have follow the implied meanings.

From the examples you share, I notice a trend in the semantics of the sentences.

The "to getting" examples are transitive. Since they are in a gerundive form, it's hard to see this, so I'll create a transitive sentence from them to make the point.

1. The Essential Guide to Getting Your Book Published -> I will guide you. You will publish your book.

2. The Guide to Getting it On -> I will guide you. You will get it on. ("To get it on" means to have sex, by the way :) ).

The "to get" forms seem to be either intransitive or reflexive. You could argue that intransitives are reflexive. For example, "I live in Chicago" means, "I do all sorts of things to myself so that my life happens in Chicago." Converting your sentences from the infinite forms to intransitive/reflexive sentences:

1. The Ultimate Guide To Get Out Of Debt -> I will guide you. You will get (yourself) out of debt.

2. A Quick & Easy Guide to get You Started Making Money -> I will guide you. You will start making money (for/unto yourself).

It would be an interesting study to see if other examples follow this pattern. It makes sense because the gerund form "getting" seems to be more active, and thus you are doing an outward activity. The infinite form seems less active, so the action is directed inwardly.

As for the example "A Quick & Easy Guide to get You Started Making Money," there is the valence aspect in the use of "to get someone started." Here is a similar semantic relationship to reflexivity. Someone (the writer) will act upon you with the result that you do something (make money). I want to think that this valency aspect might put it in the category of reflexivity/intransitivity. Just a thought.

They look pretty similar to me as meaning.

1) to getting

We say a guide to grammar, a complete guide to football, etc. The structure is a guide + noun, and "to" is a preposition. Instead of the noun we can use a gerund: a guide to understanding grammar, a guide to learning English.

2) to get

The phrase can be interpreted as: a guide (on how) to learn English, a guide (on how) to get out of debt. This is what makes the use of the infinitive possible.

Deciding which one to use (unless there is a difference between British and American English that I am not aware of) is a matter of personal preference.