Delhi is largely split into five zones/areas (not formal but geographic) and then there is the NCR (national capital region - that includes Noida, Faridabad, Ghaziabad and Gurgaon)

North Delhi - Not much to do here, nothing fancy...just the great indian middle class trying to survive the heat, traffic, pollution etc. North Delhi houses Delhi University so you'll find a lot of the city's youth in this area. There's also the chaotic Azadpur Mandi which is the hub for veggies and fruits.

South Delhi - Very posh..all the rich and famous live in South Delhi and specifically in areas like Greater Kailash (GK1), Sainik Farms, Vasant Vihar, West End etc. You'll find the 'posh' markets here like GK1 (valley girl type stuff), South ex - regular not too cheap not too expensive. Then there is Sarojini Nagar where there is....street'll find wonderful bargains here on clothes from brands like zara, gap, limited etc. They're basically export rejects but the only thing wrong with them is like....a missing label...or a thread out of place. Most college girls throng this area for colour ful skirts...spaghettis.....halters....cute clothes. On the other hand,  Dilli Haat - a MUST visit for any tourist! stalls from all over amazingly low prices! Sunday evenings will see half of Delhi lounging around in this open air market. Oh the qutub minar is here which you must visit. Cheap ticket. Inside there are lush gardens and some crumbling old buildings. Unfortunately, Delhiites do not seem to care much for this historic beauty...but you probably will love it.

West Delhi - The world lands in West Delhi, home to south Asia's largest and busiest airport, IGI Airport. Many malls and shopping areas especially Rajouri Garden, Karol Bagh, Patel Nagar and Janak Puri besides upmarket and classy neighborhoods such as Punjabi Bagh, the area is concentrated by rich business families.  West Delhi has the most famous Indian restaurant chains, a few of them from far lands of Australia as well. The region houses largest and most classy health and fitness centers, gyms, etc. and is home to the largest planned suburb of Asia at Dwarka. 

East Delhi - laxmi nagar, preet vihar, ito, mayur vihar - nothing much to do here...again..dusty and crowded like anything.

Central Delhi - CP, Khan Market, Paharganj, India Gate - This is the where you want to be. Central delhi houses the parliament and other important buildings so it's realy very well kept. big wide roads, lush greenery, gorgeous houses (particularly on aurangzeb road, prithviraj road, amrita shergill marg etc) a very bourgeois market in khan market thronged by the expat community. Check out the big chill will love it. try their home made shakes and ice creams..and their pastas....and the tuna melt. Of course, the India Gate is also here, a cherished war memorial. the lawns usually see delhiites lazing around on balmy summer nights when there is no electricity at home so mommy packs a light dinner and the whole family heads offf to india gate. dozens of ice cream vendors, baloon and other toy times for the family. no organised activity though...except for the boating....which is in a very sorry state.