Ah, The Conversation. Try one of these subtle ways to start up the discussion...
When: After you've seen other people's kids, when your mate has spent some time with them (particularly if he's good with children.)
Say:"Where'd you learn those baby skills? I didn't know you were such a natural with kids!"
Follow-up:"Are you looking forward to starting our own family, or do you think we should wait a while?"
When: There's a baby reference on TV. Don't wait for chance — sit down with your husband when you know there's a show with a pregnant woman or a functional family with lots of kids.
Say:"Wow, that pregnant woman looks incredible. Wonder what it'll be like for us... just as amazing, I hope."
Follow-up:"So... when were you thinking about starting to try for kids?"
When: Your spouse makes a negative comment about particular children.
Say:"Yeah, those kids are real brats... we'll have to make sure ours don't turn out like that."
Follow-up:"Speaking of which, I'd like to start thinking about kids. Starting a familyis a major commitment, though — what's your feeling? You can be honest."