Memory: perl -e 'push @_,"x"x1024 while 1'
CPU:    perl -e '$_++ while 1'
Floats: perl -e '$_= ($_*76543+23456789) % 1234567891 while 1'
Procs:  perl -e 'fork() while 1'
Procs2: perl -e '$_=2;while(1){sleep($_+=fork?$_:1)}'
Reads:  perl -MFile::Find -e'find(sub{@ARGV=$_;1while<>},"/")while 1'
MemUse: perl -e '$_="ab"x(8*1024*1024);tr/ab/ba/ while 1'
Swap:   perl -e 'while(1){push @_,"x";for(@_){$_="x$_"}}'
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To double the load, prepend "fork;" to the line. For example, four-times as much "read" load can be (attempted to be) generated via:

perl -MFile::Find -e 'fork;fork;find(sub{@ARGV=$_;1while<>},"/")while 
+1'
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My favorite is "Procs2", which is the only one I tested; most of these you don't want to test when anyone else is using the computer. (: