Ajax Register is a really excellent enhancement for any Joomla site requiring member registration - it was my first choice in fact.
Ajax Register met all requirements for my new Joomla 2.5 site except for just one - the IP address filtering only facilitated blocking of IP ranges, not Allowing of IP ranges.
I contacted Emir and within a few days he had modified Ajax Register to facilitate IP Allow - which is implied blocking of all other IP's - and it worked perfectly.
This is a must have Joomla Extension where you can be assured of a high quality, genuinely useful product, with exceptional support.
If you are looking for an enhanced Registration Extension for your Joomla site, look no further than Ajax Register.