Helmet suggestions

From my own googling, it looks like Giro Air Attack might fit my bill.

Can anyone report on the head down visibility with this helmet?

Also, does the shield leave enough space to wear glasses underneath it?

First, if you're struggling to see due to the helmet, then it sounds more like a fit issue... You're probably too slack to ride with as much drop as you do.

The shield on the Giro Attack doesn't leave much room... I doubt you're able to wear regular glasses behind it.

Man, are you saying this is yet another core strength issue?

It's the story of my (Tri) life ;-)

Nope, probably not core strength. I bet you're riding with the seat fairly far back (i.e. slack) which then closes the hip angle and makes it hard to ride with any significant drop. This also compresses the shoulders, which in return makes it hard to turtle your head, hence you having difficult time to see due to the helmet.

It starts with the seat position in relationship to the bottom bracket. :-)

You could buy an elastic terry headband to fill the gaps, and it ill keep the sweat out of your eyes. The fit may be a helmet design issue. Some helmets fit oval heads, while others fit squarish heads. Simply measuring your head won't guarantee the best fit. Pay a little more at your LBS to get the correct helmet since it is one of the more important pieces of equipment.

What size helmet are you running? and what brand?

Before you start altering the fit of your bike or buy a new helmet, take some time to fiddle around with the straps of your helmet and try to improve how it fits on your head, a properly sized helmet should not give you any vision issues (unless it is a TT helmet). Many helmets come in a variety of sizes, and the only way to really make sure its fitting properly is to try it out. The head measurements are very rarely accurate, and they ignore the fact that different companies' helmets all have different profiles (like different shoe companies have different lasts), which can vastly affect the fit of the helmet. Like shoes, a helmet is really something I'd recommend trying out before you buy, as one brand may fit you better than another. Hope this helps!