I have seen a lot of people searching for tools to simulate high CPU, Memory and Disk issues. Here are the tools I use

Simulate High CPU Usage

CPUSTRES.EXE is a tool you can use to simulate High CPU usage by an user mode process. Its available for download from the Windows Sysinternals website.

Here I have used CPUSTRES to simulate 50% CPU usage.

CPUSTRES also has options to change the priority of the threads it spawns.

Simulate High Memory Usage

To simulate high memory usage you can use the TestLimit tool from the Sysinternals website. TestLimit can be used to simulate a variety of memory leak issues. Here I am using TestLimit to reduce the Available memory on my machine.

Simulate High Disk Activity

SQLIO is a tool for benchmarking the I/O capacity of a given storage system. It can simulate sequential and random I/O and is usually used to test storage systems for SQL Server installations.

SQLIO is an useful tool that you can use to simulate high disk activity.

Simulate High Disk Usage

Another useful tool to simulate these issues is consume.exe. It ships with Windows SDK and can be used to consume resources like CPU, memory and disk. Here I am using consume.exe to simulate low disk space issues.

NOTE : Use these tools with extreme caution as they can freeze the machine you run them on and you might end up rebooting the machine.