y para que no queda duda de la manera en que estás usando la frase, se escucha mucho el "¿qué tal si...?" para introducir lo que uno propone "a proposito":
"A propósito, ¿qué tal si vayamos al cine?"
There are various ways of wording the suggestion in English, I'd say bloodinghard's is the least likely, as it seems to have an ulterior motive, as indicated. More usual would be "How about going to the cinema" or "Let's go to the cinema". The first can lead to misunderstandings in the group to whom its addressed, as some might feel it was an open invitation, while others regard it as purely a suggestion, hence using "Let's" which is the classic way of suggesting with a view to actually doing it, without being so formal as the invitation "Would you like to..."
It's often hard for non-native speakers to pick up the subtleties in social situations, and what is taught in lessons/books seldom tallies with real life situations!
Sorry, this is an aside, "a propósito", not really dealing with "a propósito" as the subject of the thread! - there's some ironic humour in there somewhere