Limit http request per IP

[Archi2K Archi2K <archi2k () ALTERN ORG>]

 Hi,

Last two days some people successfully made my servers crash by sending tons of random but valid http request to my 
webserver. (maybe that kind of script with wget??).

Anyway, I DENYied the C-class subnet.
Unfortunetly, I had the same problem last night with the same kind of request comin' from another subnet...

My question is : is there an existing tool to limit http request per IP?

Any help will be *greatly* appreciated!

Cheers,
a2k