build a good website with a squeeze page and then put an opt-in box on the top half and bottom half of your page
Try to launch a contest? Or offer freebies for your subscribers. Mostly, the effective ones are offering free 1 year valid anti-viruses. Technology blogs are worth the traffic.
I'd suggest designing a "squeeze page". If you aren't familiar with the concept then I'd suggest reading up on it. The short definition is a web page designed to 'squeeze' certain information out of your visitor--email address name, etc. You must present something of value to your visitors. In exchange for this thing of value they must provide you with some basic information. You should take care to put any concerns to rest about how your company will use this information. Be very clear about your privacy policy.
I wouldn't go the "buying a list" method. Follow the above advice and build a squeeze page and offer something free to download... This is the best method for building a targeted list without the worry of spamming issues. Good luck with your list