I was just registering some domains. So I was doing "whois domain.com" way too many times to find domains that were available. Pain in the ass.
Here's a small little script that will make it easier for you. 
Upload this little script to your server and name it "whois.sh"
	PHP Code:
	
		
			
#!/bin/bash
if [ $# -lt 1 ]
then
        echo "Usage:"
        echo
        echo "`basename $0` <file>"
        exit
fi
domains=`cat $1`
for domain in $domains
do
    sleep 2
    whois $domain | grep "No match for"
done 
		
	
 Change the permissions on the script "chmod 755 whois.sh".
Now upload a file with all the domains you want to check, 1 domain per line.
Run the script with "./whois.sh domains.txt" - or what ever you named the file with all the domains in. Now it will spit out all the domains that are available 
EDIT: added a 2 second pause before each whois. They seem to boot you if you whois them too fast.