*The* site to go to for anything N scale:

Sites with various tutorials:

Electrical & DCC resources:
Wiring help:
Digitrax DCC Help:
Decoder installation procedures:
Wiring switch machines:

Layout design:

Sites by fellow N-scalers:

Online Stores
Rare earth magnets:
Rare earth magnets:
Possibly the best online hobby store (they have more than just locomotives, just click on the online index link on the upper right corner):
Best prices for DCC products:
Another good online hobby store specializin in N scale:
Ready-made layouts:
Small tools:
Train elevator display: