[Johnny got his gun]

I made this modified version of antiflood.sma awhile back. Replace your old one. Make sure to have engine module enabled.

It defines a new cvar: amx_nameflood_time, default at 10.0 seconds.
If you try to change your name more often, you just can't and no spam whatsoever should be printed anywhere but on the namespamming client.
Just set cvar to to maybe 600 seconds or whatever you like. No need to change your name more often than that huh?

More cvars (new since 050110):

"amx_nameflood_maxwarnings" (default 0)
Set this to the amount of warnings that should be sent to an offender before he will be kickbanned. If this is 0 the kickban feature is completely disabled.
Ie set this to 5, and the fifth time an offender receives the "Stop flooding the server!" msg he will also get kickbanned.

"amx_nameflood_banminutes" (default 0)
This is the amount of minutes a name flooder should be banned for. 0 is permanent ban.

"amx_nameflood_useamxbans" (default 0)
Set to 1 to ban using "AMXBans", a plugin by YoMama. http://www.xs4all.nl/~yomama/amxbans/ or http://forums.alliedmods.net/showthread.php?t=1186
This bans currently with the following form in server console:
amx_ban <minutes> <steamid> "Name change flooding"