Originally Posted by rijndael
Are the external flashes, like the 430EX, a significant upgrade over the built in flash? I've seen references that the T1i flash is better than the older integrated ones.
Absolutely. Much more powerful - bouncable and faster to recharge. The power really comes into play when you diffuse the light (using an omnibounce or lightsphere flash attachment) and/or when you bounce the flash.
With such a young baby I would also encourage a wide aperture lens for lots of portrait opportunities - but that is a different focal length. I would suggest 50mm or 85mm 1.8 for your camera. The 50mm 1.8 for around $100 is a great way to get started without a huge $$$ investment. IMO the wider primes are better for environmental portraiture. But for the first year or so, IMO, most portrait shots of the baby will be very tight.