Sometimes you need to generate 100 percent CPU use, or memory exhaustion, or slow system response due to high disk I/O.
“CPU Stress” (aka cpustress.exe) is at http://download.sysinternals.com/files/CPUSTRES.zip . It can use up from 1-4 logical processors.
Need to use up all your memory? See http://download.sysinternals.com/files/TestLimit.zip . TestLimit can soak up varying amounts of RAM.
SQLIO can generate lots of disk activity. (SQL Server people like to test with it, hence, the name.) http://www.microsoft.com/en-in/download/details.aspx?id=20163