Unless you are talking about weight loss, insurance, make money online etc. you can pretty much take on any niche and rank in 4 weeks with good SEO.
If you are thinking of throwing a website and ranking for it and getting lots of traffic without any SEO... well those days are gone.
Firstly though you need good keyword research using a tool like Market Samurai. You can find lots of long tail keywords that are with very low levels of competition in most niches with good keyword research.
Secondly, good content that is unique. Don't expect to scrape content and then rank better than the original source.
Thirdly, you need to do SEO using tools like SENuke or something similar.
If not SEO then check out other options like Twitter, PPC, PPV, Facebook, etc.