Add content after the latest post on the archive page?

Hey,

I would like to know how I can add content/a title/an image/function/(really whatever) after the latest/most recent post on the archive page?

A client asked me about this recently, so I thought it might be good to know for future references. It might also be a help for other developers who want to add ads on their clients websites.

Thanks a lot!
Sincerely,
Mika