A helpful list of conversational topics.
1. Who's a big [girl/boy]?
2. Show me your teeth!
3. Where's [mommy/daddy/family pet]?
4. Patty cake, patty cake, etc.
5. Shake it! Shake it! Shake it! (encourages dancing and/or jazz hands)
6. Clap for [baby]! Yaaaaaay!
7. Oh, you're so busy, baby! Busy baby!
8. Where are [baby's] ears? (repeat with other facial parts)
9. Ahhhhhh BOO! Ahhhhhh BOO!
10. Say CHEEEEESE! (approach webcam with face while repeating - this generally gets a big laugh)
11. One, two, buckle my shoe. Three, four, etc. (present corresponding digits to the web camera while reciting)
12. Where's your [dolly/truck/favorite toy]? Show me your [etc.].
13. [For babies old enough to approach and stand at baby gates]
[Baby's] in jail!
[Baby's] allowed one phone call!
Where's [baby's] lawyer?
[Mommy/daddy] didn't read me my Miranda rights!
14. Do you want a cookie? Ask [mommy/daddy] to give you a cookie! (watch baby turn around in earnest at parent, start to melt down when said cookie does not materialize)
15. How big is [baby]? [She's/He's] sooooooo big!
16. Say bye-bye! Bye-bye, [baby]!
Above list applicable to babies 3 months to 1 year.