Doors:
The cabinet doors come in 4 different heights. Those heights are, in turn, available in varying widths as follows:
door Ht 30 1/2: widths 12", 15", 18", 21"
door Ht 23 7/8: widths 12", 15", 18", 21"
door Ht 17 1/2: widths 15", 18", 24"
door Ht 14 7/8: widths 15", 18", 24"
Please note that the precise door width was about 1/8" less than the widths I've listed (e.g. a 12" wide door is actually about 11 7/8" wide). Also note that the 30 1/2" Ht is used on base cabinets with no drawers. The 23 7/8" Ht is used on base cabinets with one shallow drawer at top. I did not measure wall cabinet doors (so I guess you could add all the 39" height doors to this list).

Drawers -- OUTSIDE measurements:
All shallow drawers = 6 1/4 Height
All deep drawers = 11 1/4" Height
Like with the doors, the precise widths of the drawers were about 1/8" (maybe 1/4") less than the listed width. E.g. a drawer on a 24" wide cabinet is about 23 3/4" wide.
Please note that because of these drawer heights, you CANNOT use all shallow drawers in a drawer stack (I had been hoping I could for the 21" and 24" wide base cabinets :( . )

Drawers -- INSIDE measurements:
ALL drawers (shallow and deep) = 19 3/4" Depth
This is measurement from inside of drawer front to inside edge of drawer back.
All shallow drawers = 5 1/4" Height
All deep drawers = 9" Height
Here, I measured Height from the bottom of the drawer to the top edge of the drawer on the inside, so I knew how high I could pile stuff inside the drawer and still be able to shut it!

Inside Width of Drawers:
This was a little tricky. As you may know the bottom of the drawers do not form a 90 degree angle with the sides. There's a slight curve there. The drawer sides also slope out a little from the bottom to the top. I wasn't sure which measurement I would later need, so I took 3 different measurements: (1) the white bottom that's completely flat, (2) the bottom including a little bit of where the bottom curved into the sides, and (3) from the top inside edge of one side of the drawer to the top inside edge of the other side.
Shallow W15: (1) 10", (2) 10 5/8", (3) 11 5/8"
Shallow W18: (1) 13", (2) 13 5/8", (3) 14 5/8"
Shallow W21: (1) 16", (2) 16 5/8", (3) 17 5/8
Shallow W24: (1) 19", (2) 19 5/8", (3) 20 5/8"
Deep W15: same widths as Shallow W15
Deep W18: same widths as Shallow W18
Deep W30: (1) 25", (2) 25 5/8", (3) 26 5/8"
Deep W36: (1) 31", (2) 31 5/8", (3) 32 5/8"

The top shallow drawers on the 30" wide base cabinet are simply 2 x 15" shallow drawers (and 36" has 2 x 18" shallow drawers).

Corner cabinet (regular, not blind corner):
Forgot to measure door. Did make sure the steel lazy susan shelves can be moved to different heights. Also, there are no fixed shelves that fit in this unit, even shelves that would be used only on one side.

Oven cabinet: I was needing to know what size oven I could fit. The sides of the 30" oven cabinet (like all cabinets) are 3/4" thick. That means the opening of the oven cabinet is 28 1/2" (=30" - 3/4" - 3/4"). When you get the oven cabinet, it comes with a solid piece of cover paneling that covers the WHOLE opening of the oven cabinet. You then cut out whatever your oven directions say is the cut-out. So as long as your oven cut-out is less than 28 1/2", you should be okay width-wise.

Horizontal wall cabinets: These are NOT the same width as the base and wall cabinets that are 30" wide. The horiz wall cabinets are actually 30 1/2" wide. They are, therefore, WIDER than the 30" wide base and wall cabinets. I was hoping I could use some of these doors on a high cabinet that I'm using for a desk. Alas, they are TOO WIDE. This of course means that you cannot stack them on top of the 30" wall cabinets and expect them to line up on both sides. The reason they're like this: they're actually a 15" wide base cabinet turned sideways (and the base cabinets are 30 3/8" high).

Cover panels:
The cover panels are all 3/8" thick EXCEPT for the one listed as: Cover panel for base cabinets 24 1/4 depth, 3 x 8 feet. That cover panel is 5/8" thick. It's what people on this forum call the Oven Panel (I think), and it's what's supposed to be used next to appliances (eg dishwasher, fridge) where there's no cabinet to attach it too.

Okay, I apologize again for the length of this. Way too Ikea detailed. I have to add funny story: DH & I went to Astros game the evening of our Ikea adventure. I still had heavy duty tape measure, ruler, wood sample, etc in my purse. The security guard who searched it laughed and asked: "Doing construction later tonight?" I'm pathetic :)