Industry recognised job boards such as Reed and Jobsite attract candidates to apply to adverts and also upload CV's to a searchable database.
Linkedin premium services offers an amazing database which allows for granular candidate searches (industry, years of experience, complex boolean) . Candidates can identify themselves as 'open to new opportunities' or simply leave a profile, waiting for a Recruiter such as myself to send a personalised mail to entice them.
ContactOut is the market leading service which can identify connect Github accounts and email addresses with Linkedin profiles which offers a further boost to personalisation to approaches.
Career Concept has subscriptions with all these services and also resources from our own database of candidates