If you were going to give a list of something/people, would you say:

'In the name of myself and the rest of my colleagues...'

or

'In the names of myself and the rest of my colleagues...'

and why?

Mmm, this is an interesting one. I can see the argument for both, but I prefer "In the name of...".

I think it covers it. "In the name of" is a set phrase. Consider this sentence: "In the name of the people of Zorkon..."

Now, people is plural, just like "myself and the rest of my colleagues". Therefore, as a set phrase with a specific meaning, I do not think it needs to be pluralised. I do not consider either to be wrong, but I prefer "In the name of". I would leave "on behalf of" as singular too in a similar sentence. Grammar is not always black and white, I'm afraid.

Thanks! :)