I live in the city center so here is what I find myself doing a lot:
Bars, lots of bars. I work as a barman so find myself going to a lot of different bars. The Northern Quarter has a lot of great independent bars, restaurants & cafes as well as shops. A few good places are:
Matt & Phred's which is a great live jazz & blues bar, people often turn up with their own instruments to jam.
http://www.mattandphreds.com/
Port Street Beer House is incredible if you like beers, they have the biggest & best selection I have ever seen. Just have a look on their site
http://www.portstreetbeerhouse.co.uk/
Luck, Lust Liquor & Burn is great for food with a menu ranging from the States to Central & South America, it has a great bar as well. There is a new bigger one down by All Star Lanes (see below). Luck Lust now has
Almost Famous' burger menu since it burned down (cries inside), if you like burgers than make an effort to go, they are simply incredible.
Brew Dog also has a bar near All Star Lanes which has a great choice of beer.
Trof does great food & is a very popular bar in the evenings, I go there a lot as they have the biggest bourbon bar in the city with some great offers.
Hula, Keko Moku & Liars are all great Tiki bars. Read Tiki as rum bars with great music, people & very much of a big party vibe to it. Liars is the other side of town with
Mojo's above it which is one of the best bars in the city for it's music & atmosphere, both are late night bars. People tend to go to Mojo's first then head down to Liars where it all gets a bit nuts
Finally for something a bit different,
All Star Lanes &
Dog Bowl are late night bowling places. Both great for food & drink. There is nothing quite like bowling until 4am whilst drinking White Russians
For some more up market bars/ restaurants head to
Spinningfields for Alchemist, Australasia, Grand Pacific & Oasthouse. Oasthouse was originally ment to be a old style pop up bar in the middle of the financial district of Spinningfields but it is doing that well it is now a permanent feature. All great places with some magnificent food and drinks. A quick google will show you what they are like.
Australasia & Grand Pacific have some exquisite food. Spinningfields is also home to some of the more expensive shops in Manchester.
As has been mentioned, check out the museums & art galleries if you are in to that sort of thing. They always tend to have some great stuff on.
If you have never been to an IMAX cinema than head down to the Printworks Odeon. Currently in the IMAX Elysium is playing and....wait for it....
JURRASIC PARK!!! It's a bit pricey but always a great experience.
I'm at work at the moment, that's what I can think of off the top of my head so when i think of more stuff I will add it. If you have any questions feel free to ask.
One final thing,
don't go to the Printworks for anything other than the cinema.