This one:
Lenovo
Ideapad Y580, i7-3630QM + Nvidia GTX660M + 1920x1080 @RM2999[JBL], 4GB, 500GB(5400rpm), W7HB/W8, backlit keyboard, 2 yrs warranty (Stock limited)

CPU & GPU powerful enough for all your video editing and photoshop/lightroom.
Stock is limited, going to EOL soon, grab it quick while you can

You can upgrade RAM (or ask the reseller to help you), 4G stick ~RM80. It will not void warranty if you do not accidentally damage warranty stickers inside the laptop (normally there is no warranty sticker near RAM slot).
How much RAM a laptop can support depends on:
a. OS - if you use 32bit OS, anything above 4G could not be utilised. W7S, W7HB, etc also has limitation.
b. RAM slots - most laptop has 2 / 4 RAM slots. If the laptop has 2 RAM slots, and 1 of them is occupied by a 4G stick, and you want 16G, then obviously you need to get rid (or trade in) the 4G stick in order to fit in 2x8G. RAM in some ultrabook are fused onto motherboard and has no RAM slot for expansion.
c. Memory controller - this used to be on motherboard, but Intel i-core CPU (like so many other CPUs) has integrated memory controller. Without going into too much detail, if you go i7, your laptop will be able to utilise 16G RAM.

Errr ... how could we help you unless you tell us where you are?
Lenovo don't sell online in Malaysia.

Inspiron 14R (Special Edition), i5-3210M + Nvidia GT640M(28nm Kepler)@RM2049[2.38kg], 4GB, 500GB(7200rpm), W7HP/W8
This is one of the laptop in Malaysia with most raw power at RM2k price point. Now whether it is enough for you, I really don't know, because I don't know how "heavy" is your video editing