Spam registration

Not sure if this has been brought up before but I am getting a huge amount of .ru and .gmail registrations,these are not being activated but are loading up my database.
Not allot of them on average 20 to 30 every 5 or 6 days.
I have Akismet enabled, It is really not a big deal just annoying having to go in and delete them.
Anyone have any ideal how I can fight this.
Thanks
Chris