CONECTIVOS DE INTRODUÇÃO OPORTUNA DE ASSUNTO RELACIONADO
Servem para apresentar um assunto relacionado, em momento oportuno; "aproveitar o gancho"; fazer uma observação complementar.

EXEMPLOS:

Ricardo Schütz
Atualizado em 20 de fevereiro de 2014
  
 
    
A propósito, ... / Por falar nisso, ...
By the way, … / Speaking of that, … / Incidentally … / As/On a side note, …
a propósito
  Excelente o seu artigo. A propósito, você me autoriza a imprimi-lo e enviá-lo para algumas pessoas amigas?
  Sobre a presença da língua portuguesa no mundo, existe um estudo do Instituto Camões, entidade vinculada ao Ministério dos Negócios Estrangeiros de Portugal. A propósito, você sabe quem foi Camões?
  Quando, em 1492, Colombo chegou à América, encontrou vários povos e civilizações em estágios diversos de desenvolvimento. A propósito, você sabia que ao chegar ao continente desconhecido, Colombo achou que estava chegando à Índia, e que, por esse motivo, passou a chamar os nativos de índios?

por falar nisso
  A sociedade humana está cada vez mais doente. Por falar nisso, você sabe quantos morreram hoje no Iraque?
  Assim como o Khouri, outros grandes diretores paulistas precisam ter suas obras devidamente reavaliadas. Por falar nisso, você é de São Paulo?
  Nunca fui muito bom para decorar datas de aniversários. Por falar nisso, lembrei-me agora que o meu avô fez aniversário ontem e nem lhe dei os parabéns.
by the way (less formal)
  We are expecting freezing temperatures for the next few days. By the way, did you bring warm clothing?
  He'd had dentures since he was twenty, very bad ill-fitting ones, by the way. They made him self-conscious and he wanted a new set. I asked him why he'd lost his own teeth and he said the cause had been pyorrhea.
  The car is made to run on standard unleaded petrol, but it may run even better on Super Plus unleaded. You won't hurt the engine by trying -- only your wallet. By the way, I deplore the practice employed by some filling stations of having several premium unleaded pumps on the forecourt but tucking the standard and cheaper fuel, away in a corner.
  “You are a married woman,” he said to his wife in his best imitation of an authoritarian voice. “If you must write – you don't need to by the way, I can earn enough to support my family – but if you really must, you should always write "Mrs. Nigel Hughes" at the end of it and tell the editor you are married to me.”
  He dropped a gallon of emulsion paint in an 800-gallon lungfish tank, then had to completely strip and redo the tank out late one night. The fish survived by the way.

speaking of that
  With Senator Akaka, we all serve on the Veterans' Affairs Committee as well as the Veterans Appropriations Committee. And speaking of that, Senator Craig, the chairman of the Veterans' Affairs Committee, has been a real leader here as well in trying to work this through.
 

To be able to shoot a film in space would be really exciting. Speaking of that, I’m going to space in 2008. Richard Branson is building this Virgin Galactic Space craft, and I’m one of the 100 founders. We are the first to go up; the guinea pigs!

  Anyone who writes a program can distribute it through any means available, such as through the Web or by sending you a copy. Speaking of that, have you ever received a CD-ROM in the mail?
  A design that is functional and sophisticated with all the bells and whistles but costs way too much is not a good design, in my opinion. An $800 phone, for example. And speaking of that, when will someone design a portable phone that just makes phone calls?

incidentally (more formal)
  In examining the CIA's past and present use of the U.S. media, the Committee finds two reasons for concern. The first is the potential, inherent in covert media operations, for manipulating or incidentally misleading the American public. The second is the damage to the credibility and independence of a free press ... (Frank Church, 1975)
  I'm on vacation and I've taken the precaution of leaving all my nursing manuals at home. If you're going to take a break it may as well be a clean one. Incidentally, have you been to the kibbutz library yet? They've got some very interesting works.
  The airlines charge half-price for students. Incidentally, I have already bought my ticket to New York.

as/on a side note
  The man was wanted for tax fraud and for operating a bar without a license. As a side note, he had been running the park without insurance.
  If you want to leave the box plain, go ahead and seal and paint (or varnish) the box and lid. Be sure to thoroughly seal all the plywood edges! As a side note, I like to seal plywood edges with epoxy; in fact, I use epoxy to glue all the parts together.
  When was the last time you were at a meeting when someone wasn't thumbing a BlackBerry or iPhone to "talk" to others, asked gaming development professor Scott Leutenegger. Teenagers aren't interested in separate, old-style cameras, he added as a side note. They simply snap smartphone pictures of everything they see, and post the images instantly.