[consulting] user registration and auction

[Hasan]

Dear Sir,

I would like to ask about the available modules for (User registration). 
The User will be able to create new account (customizable fields) 
including CAPTCHA field and send conformation email. Then the User will 
log-in and participate in online Auction.


Please, list the modules which are able to achieve the above things and 
which one do you recommend.

Regards,
Hasan