There are general guidelines, but they're just guidelines because there are usually many variables at play.

In general, you might consider hanging the kitchen island lights @ 6' above the floor (some say as high as 6'-6"). You don't want them at eye level (may need to adjust if family taller than avg).

For the two-story foyer there are a few thoughts: @ 5' from the ceiling, not below the second floor, or so that it shows through the window.

Hard to tell without being in your space, but hopefully these general guidelines are somewhat helpful. I am usually on site for installation so that I can eyeball any adjustments.

One trick is to hang balloons on strings from the ceiling to mock up where the lights will hang. You can then test the sight lines from different angles. (Simple, but it works.)

We have our island chandelier base at 36" from the granite. Works for us. I hated it when we mocked it up lower. We have our dining room chandelier 30" from the table top though, and I like that b/c it makes it more intimate. I've never heard the 6' thing for hanging lights...only for sconces. As far as the 2 story foyer, IMO, it really depends on the size of the light, size of the overall space, ceiling heights, etc. We have 9' ceiling heights on both floors, our foyer chandelier is 65" in height and we have it hanging approximately 3'6" from the ceiling. We would have gone slightly lower, but our staircase winds down through that space, and I didn't want anyone to be able to touch the chandelier!

http://www.masterpiecelighting.com/designideas.aspx

This link has some general guidelines for fixture height and size.

dixiedoodle, Are your countertops standard 36" off the floor? If your chandelier base is 36" off that, it is at the 6' guideline. :)

athensmomof3 posted a good link. There are actually lots of lighting stores that can give you similar general guidelines. They may vary a little, but they are still helpful.

Disclaimer: I'm an interior designer. Just joined the forum.

We are a little over 6' off the ground.

Over an island it depends on the fixture and how the island will be used. If there is seating at the island they should be low enough that the lamps are not shining in your eyes when seated and high enough that they are not blocking your view when standing. That can be difficult to achieve unless the fixture has a screen or lens on the bottom.

I usually use low-voltage pin-hole recessed spots and avoid the issue. IMHO If the kitchen is well designed, pendants add little to it. I guess they also remind me of the original "casual modern dining" prototype popular in the late 50's or older billiard table lighting.

Our pendants are on the small side and are 36" above the island, just seems to work for us. As for the chandelier in the foyer, we have a large palladium window there. I moved it so it was perfectly centered in the window from the view in the street out front.

Thanks guys for all of the info
The pendants we got are 48" in length, so we had no choice in how high to hang them. They are a peferct height actually, it hink it works out to be about 30" above the island since we have 9 ft ceilings and the island is about 2.5 ft tall
As for the chandelier, just as limcufsem said we centered it at the large window