These are a few sites I visit a lot.

Pojo Network This is a great site for just about any anime imagineable.

Yu-Gi-Oh Haus This is a great Yu-Gi-Oh card site.
Crosstoy.com This is a good on-line anime store.
Edo's Yu-Gi-Oh! Page! Edo's site is a good yu-gi-oh site. He has translations and information on just about anything yu-gi-oh you want.