My Necron army list:

2 Lords
20 Immortals
35 Warriors
23 Scarabs
10 Destroyers

This is about 2000 points.

Usually I tend to field the 20 Immortals and 30 Warriors for 1100 points. Everyone has trouble taking down these 50 necrons. Hehe. The army gets accompanied by 2 Lords usually. When faced against an assaulting army, deploy as close to starting line as possible. Then take cover and move backwards to maintain shooting. You want to shoot your enemy AS MUCH AS POSSIBLE with Necrons.
Stack troops up as you need... go box formation like having 3 to ranks of 10 guys.

My Tyranid army list (it's in the works):

1 Hive Tyrant
1 Zoanthrope
1 Biovore
1 Carnifex
2 Lictors
24 Genestealers
18 Termagants

Some useful gaming links:

PORTENT, a VERY good source for Games Workshop product rumours and related stuff.