Very basic one:

perl -e 'while (++$i) { $foo[$i] = $i; }'
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That'll chew memory like mad, and soon bomb out. CPU usage minimal.

of course, you can make it use CPU...

perl -e 'fork; fork; while (++$i) { $c .= crypt($i,$i); $c = substr($c
+,4,128); }
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Ctrl-C kills all children, no root required! Load should fly up to around 4, give it a minute or two. To add mem usage, change the substr length.

Fun request!

Trinary