If you go to
www.spark-plugs.co.uk put in the relevant details, and you'll see what are the best plugs for your car.
I believe the OE plugs are NGK platinum tipped (PFR7B). Personally I'd go for the BKR7EIX from the NGK IX range (Iridium tipped) or Denso IK22's, for the standard car ! The NGK's are the cheapest and actually cheaper than the OE platinum tipped plugs. The mentioned site is also the cheapest place to buy plugs for the GTiR from !
As above with the oil, Silkolene Pro S 10w/50 is the prefered choice. I've used Mobil 1 15W50 and Motul 15w/50 in the past, I switched to the Silkolene and there's a noticable difference in how loud the engine is and how smooth it feels. If you email the oilman your details and user name, he'll send you access details to the 'members section' on his site. He's currently running a discount on all his oils until 5th October !
When you change the oil, use and OE Nissan oil filter !
Oh and yes, the search function is nigh on useless !