loads to do! Looks like your in a good location in midtown - fairly central your just on the east side. Some decent shopping around Madison and 5th avenue but its better down in Soho.
If your looking for bargain shopping Woodbury Commons is good but about an hour drive away by bus but is full of bargains but takes up a full day.
Some great food to be eaten everything from cheap mexican, pizza, diner\delis to high end michelin star stuff which is pretty good value. I ate at gordon ramsays at lunch time in November and it was only $45 for 3 courses. Try
www.menupages.com for a choice of over 6000 restaurants which you can filter through on types and food and location.
try and use the subway as much as you can as its much quicker than getting cabs or buses once your figure out which way to go. However you can walk most places in midtown and the park and after 8pm cabs are good as the traffic dies down a bit. Its only really for getting down to SoHo, Brooklyn Bridge and greenwich village
Central park is a must - brilliant in the summer and will be absolutley chocker especially at the weekends.
Most people recommend the empire state building but its always dead busy - try the rockerfellar centre instead as you get better view of the park and can get great pictures of the empire state building too.
I think there is a temporay beach thats been built over the river from Manhattan in queens at long island city which you can get to using nywatertaxi.com
Loads of bars - too many to talk about. Fiddlesticks is a good one in greenwich village and run by a lad from liverpool\wirral, loads down bleeker street and east village. Irish bars are a good place to start as they usually full of people who can point you in the right direction.
Tonnes of museums as well if thats your thing. Natural history musueum good, also the Tenement museum in the lower east side is something a bit different. Might be worth checking ticketmaster see who's on.
Little Italy is worth a look and Katz deli on Houston street sells the best sandwich you'll ever eat!
Also try and get to a Yankees game or the Mets chances are there will be at least one on while your there.