Siege

siege -b -c=10 -t=5m http://...

-c, --concurrent=N
-t, --time=MINSm
-r, --reps=N

-i, --internet       Hit URLs randomly
-b, --benchmark      No delay between requests

Configuration

-f, --file=FILE      load urls.txt
-R, --rc=FILE        load siegerc

Also see: siegerc

Headers

-H, --header="Cookie: foo=bar"
-A, --user-agent="Mozilla"
-T, --content-type="text/html"