You're blog doesn't have to be about saving money, coupons, or even deals. If you love to cook, you can post recipes and food-related articles that even the novice cook will enjoy. Are you a crafter? Post your craft triumphs and failures. If you have a family, you can become a mommy blogger, posting about the tribulations of raising children. So how do you find out which niche your blog will work best in?
Take a look at what you enjoy and what you have to offer. Every single blog is different because while they may post some of the same things (like offers and freebies), they all have different posts about their children, families, or whatever tickles their fancy. If you are savvy at saving money but have a family of 6, readers who have big families will want to hear what you have to say. Don't understand the whole "reviews and giveaways" thing, you don't have to be part of that niche. Blog about what interests you and what may interest your readers.
Keep in mind that you don't have to find a niche for your blog right now. Post what makes you comfortable and you will eventually find that category that your blog belongs in.
Even if you never find that category that has already been created, create your own! I know of one blogger who has a food and craft blog and does very well. Do what makes you comfortable and don't feel that you have to change your style of blogging just so you can fit into a certain category. That's what makes blogs unique- their writers and what they write about!
Next on Blogging 101: Blogging do's and don'ts!