Perhaps the loveliest, at least from a parents point of view, is that he can now tell us when he's happy. Not just a smile, but a coo-gurgle-mehch (that's the nearest approximation I can manage) and a smile. If he wants more attention, he looks at you and eh-ohs. Often, just looking back at him and repeating "hello" after each "eh-oh" is enough to send him into fits of delight. His eyes twinkle, he grins like a madman and he wriggles about in a coquettish fashion. It's almost as if he's having too much fun, and has to break off eye contact to calm down. Seconds later though you'll hear another "eh-oh" and the whole process starts over again.
Alex is very definite about when he wants to look at you. If he wants to play, he'll let you know. If he doesn't, nothing will make him make eye contact. Often he'll want to be held up by the armpits and helped to "stand". You can either hold him facing you, or away from you. If he's in a non-communicative mood and you hold him facing you, he'll twist his head through 90 degrees to avoid looking at your face. At times, it gets a little Excorsist-like. We've taken to holding him facing outwards when he's in that sort of mood. It's less fun for us, but looks a lot less sore for him.
It's curious how expressive a baby can be, given the limited range that gurgle/flail/scream has. The difference between a happy flail and a bored flail is as clear as night and day, yet there's nothing specific I could point to that distinguishes the two. Similarly, the "I'm having a great time" squeak and the "I'm about to turn bright red and puncture your eardrums" squeak sound utterly similar but are totally different. It must be a mixture of body language and familiarity, but it seems like magic right now.