there are plenty of good trails in newcastle.
it just depends on what you ride xc or dh. glenrock has short dh trails and some great xc rides. you can normally find people there most days.
killi is similar to glenrock but not as many peolpe there on a regular basis like glenrock as it is further away from town.
then there is awaba which has a killer dh trail and the xc is currently being built.
enjoy your riding, hope this helps.