Q:

How to make the hottest CPU temperature?

Besides just running an infinite loop, are there any tricks (like maybe cache misses?) to making a CPU as hot as possible?
This could be architecture specific or not.

A:

I have produced several reports on stress testing PCs via my [Free] reliability/burn-in tests for Windows and Linux. You can find the reports through Googling for “Roy Longbottom burn-in”.
What you need is a variety of programs that run at high speeds to test CPUs, caches and RAM. They should log and display speeds at reasonably short intervals with temperatures noted or preferably also logged. On running them, you can find which are the most effective. You can run multiple copies concurrently via BAT files for Windows or shell scripts with Linux, rather than relying on more complicated multithreading programs. You also really need programs that check for correct results of calculations. For system testing, one of the programs can use graphics. Here, for nVidia, CUDA programs are useful in producing high temperatures.
Following shows CPU core and case temperatures before and after blowing out the dust from the heatsink.

Following are results on a laptop, testing with data in L1 cache. These show variations in speed according to temperature. Other CPUs might be more affected by different data/instructions/which cache is used.
  Overheating Core 2 Duo Laptop 1.83 GHz
 Words      5K              5K
Ops/wd       2              32
          Core  MFLOPS    Core  MFLOPS
Minute      °C      x2      °C      x2

   0.0      65              65
   0.5      96    4716      91   10168
   1.0      98    3362      94    4756
   1.5      91    2076      87    4443
   2.0      87    2054      86    4452
   2.5      85    2054      85    4235
   3.0      84    2036      84    4237
   3.5      82    3098      83    4376
   4.0      89    4773      83    4420

You might also be interested in my Raspberry Pi tests (Cooking The Pi), where the RPI is overheated via a 60W lamp, to crash when overclocked and show speed variations that vary with temperature.  Here, the CPU integrated graphics is the most demanding hardware.
http://www.roylongbottom.org.uk/Raspberry%20Pi%20Stress%20Tests.htm#anchor7

A:

Since modern CPUs are usually power aware, they have many builtin mechanisms to power down whole parts (cores on a multicore system, or even internal units within).
In order to really stress the CPU, you need to make sure you activate as many units as possible. 
This can be most easily achieved through heavyloading your vector execution units if you have some, or floating point ones otherwise. On the memory side, try to constantly consume as much bandwidth as possible in order to stress the memory unit, caches and memory buses. Naturally, run your code on all available cores (if hyperthreading is available it might be a good idea to use that too)
This type of benchmarking is commonly known as a power virus. There are several examples over the web, you can look up cpuburn for e.g. (it has some sub flavors)

