If you are wanting to join some giveaways to build your list, then here are several sites that you should definitely visit:

http://www.giveawaygallery.com/
http://www.newjvgiveaways.com/
http://www.eauthorresources.com/giveawaylist.html
http://www.giveaway-list.com/

The sites above list the current and future giveaways. Keep in mind that you're not going to "hit a home run" with every giveaway. It's possible to pick up as many as 5K subscriber through some giveaway event while you'll be fortunate to pick up 200 subscribers at others.

You will need a good 'gift' that you can offer in the giveaway. My suggestion is to take a plr product & make a variation of it. That way you can offer an exclusive product not available anywhere else. Not only does that make your product look more attractive but it also brands you as an expert in your niche.

Here a free software that you will find helpful in lead generation:
http://www.leadscouter.com/

Thanks,
Mark