It's definitely Vivocity - It's the last station of NEL. From economical variety choice of shops to the high (not very but still consider high end) kinda shops. U can get bargain stuffs at $2 at #3 - Daiso and high end like Amani Xchange. :)
For food, they have many restaurants - food courts at 2 levels: B2 and Level3, and also if you have the extra money, there's nice and wonderful restaurant catered for you - Swensen (Earl's something), Dian Xiao'er (YUMMY chinese rest... it's a MUST try)... and if you want a good kick of Fast food, there's Superdog, Subway etc. They have good place for wine and all too, which is the building beside Vivio aka Harbourfront centre. :)
Big supermarket like Giants (good bargain sort), Cold Storage, etc. :) And if you like to have a break, you may go to level 3 and enjoy the scenery of Sentosa just opposite Vivo, and you can take a monorail ride over. :)
If you're looking for books, there're one or two bookstores over there and also, they sell great variety of electronic gadgets... but it's always too ex to get there because their rental there is super high. So if you want to get any, go to Sim Lim Square... - good and cheap bargains. go to level 4 and above... Cos level1-3 are tourists spot and the locals will just raise the price to earn something from the tourists. Haha, it's not con, but just that this is how locals earn from tourists - in every country.
If you need a good drink, I'm sure there's some restaurant having promotions over there at Lvl 1, not sure what's the name of the restaurant called but it's near 'Dockers'. :)
They have big-screened movies cinema(Golden Village). and it's really good!!! :D Trust me. Or go down to Dhoby Ghaut - Cathay cinema if you want to experience the same sort of comfy.
Or along the NEL, you can go Clarke Quay to experience the nightlife. Somewhere near Vivo, there's great club/pub called: St James powerhouse. So thus I guess that's why everyone's answer is VIVOCITY. Another is Plaza Singapura - a place where most youngsters hang out. There's 2 big cinema theatres and don't expect much of luxury products. Oh it's at Dhoby Ghaut. :) U can go there from the REDLINE or the Purpleline which is the NEL.
Actually, it depends on what u are looking for. If you wanna feel the 'warmth' of the local mall, u may drop by at any heartlander's malls from : AMK hub, Bishan Junction 8, CompassPoint at Sengkang (no cinema though), Jurong Point, etc. :) Most of them have cinema theatres but you can't expect much like branded shops over there. :)
Yea, if you wanna get more shops, go Orchard Rd... Higher ends of shopping: Paragon, Takashimaya - the other end of it, CK Tang... If you are into young fashions, you can go to Far East plaza at the other side of Orchard but it's just about 10 mins walk from Orchard MRT stn. :) You can find loads stuffs over there. :) Or even Bugis stn - Bugis Junction... where most youngsters / youths / young adults hang out!!! :D
Over there in Orchard, there's also SkatePark (Somerset mrt), where u can see guys skating and all. :)
If u are into Arts, u can visit museums and even high-end arts at Esplanade... :)
Hope this helps. Cheers :)
Enjoy your stay!