What about batteries?
If I were to try and hide a bomb today... I would build it into batteries. You can store explosives and biochemical weapons in batteries really easily.
Let's use a D sized cell as an example (it works with all other types too). Whatever you place it inside of needs to function on one less battery as this battery is a fake. It doesn't have to function well... if you're asked, just say "I'll buy new batteries when I land. It's too expensive to buy them in the airport.".
Using a dense metal, you machine a device in the shape of a D-cell to a high precision. It be a screw off design with a heavy, soft rubber gasket inside. Pour a thin coating of melted lead inside the unit. This should make it look like a real battery and hide the contents from X-ray machines. Fill the fake battery with the deadly chemical of your choosing. Then close the battery so that the seems aren't visible.
Now, the problem is, you've got traces of the toxin all over the battery on the outside. Depending on what toxin is used, the battery will need to be cleaned appropriately. Sterilization will only work on most, not all. For example, it won't hide magnesium on the outside. You'd have to file that off.. or machine off a little metal and then sand it and then sterilize it.
Now, carefully remove the outside coating (containing the advertisement) from a duracell or energizer battery and apply it to the new "battery". If it doesn't look right, do it again. What's 2 bucks when you're going to be dead in a few days anyway.
What you have now, is a battery that you can put in a flash light or in a radio or whatever that will go through X-Rays and bomb detectors undetected since all the chemicals in batteries look like bombs anyway. They are after all toxic chemicals.
So... what I'm saying is... they shouldn't let ANYTHING with a battery through security since there's no possible way a new X-ray machine or detector could possibly be designed that could tell the difference between a bomb and a battery.
Laptops are even better for this... they often contain 6-12 batteries and it's easy to say "oh... I'll charge it when I'm waiting for my flight". iPods, iPhones, etc.. are good too since their construction is good enough that no one would even think to look for a bomb inside of one of those and you could get to the bomb by "breaking the glass" and tearing it apart.
Curling irons are also great since the heating core of a curling iron is a great place to hide things from detectors.
I can think of tons of different places you can hide things.
Of course... the "detector companies" aren't about to raise red flags on things they can't build fancy new machines to detect through. So... the only thing that can be done... for safety sake is to ban all battery powered electronic devices from flights. That means, no phones, no computers, no radios, no music players, no dvd players etc...