I would go for a 15.6" laptop, because it is still portable but you can also get good specs with those. Ultrabooks have no dedicated graphics, only the intel 3000/4000 graphics which won't allow you to game. The processor is usually also some sort of u version of intel which runs under 2 Ghz but gives you a long battery life.
I bought a new laptop a week ago for university next year. After looking through loads of laptops and specs it turned out that a Asus N56vz laptop would be the best choice for me :P
http://www.asus.com/Notebooks/Multim...ainment/N56VZ/
i7 3610QM Processor (2,3 Ghz - 3,3 Ghz)
GT 650m videocard (2 gb)
8 gb 1600 RAM
Full HD screen is what I went with for programming and it has been a great choice.
The sound quality is very nice aswell, nearly as good as my desktop speakers which is impressive for a laptop.
Other laptops I went through:
MSI Ge60
GIGABYTE P2542G
Lenovo Y580
Dell Inspiron 15R SE €900
Dell Xps 15 2012
Dell Xps 14 2012
Asus N56VM
MSI Ge60 has the GDDR5 version of the GT 650m which is definately an impressive graphics card :P I haven't done any gaming on my laptop yet with the GDDR3 version, but that one should be nice for a laptop aswell.