I'm looking for a website that let me localize IP address (at least country, town and ISP would be a plus) without limitation.
I would like to enter several address (as this site does : http://www.ip2location.com/free.asp) from browser.
I would guess that you are going to struggle to find a free and unlimited service.
I would think that the lookup process is quite expensive either in terms of the processing and/or bandwidth required or these people get charged by their provider, so allowing anyone unlimited lookups would incur monetary penalties.
If you need more than 20 lookups per day then you should really look into paying for the service.
Why not just use the free Maxmind database's (both Country Lite and City Lite). You can download them and set them up for free on your local server. That way you can go to town and don't have to worry about any limits.
GeoLite Country: http://www.maxmind.com/app/geolitecountry
GeoLite City: http://www.maxmind.com/app/geolitecity