The silver tie clip and the gold one are your two main options. Like always, choose the color that goes best with your skin and the color of the shirt and suit.
Gold goes best with darker complexions and silver goes better with light complexions. Also remember to match the color of your belt head, watch, and cufflinks to your neck piece.
When buying new items for your wardrobe keep in mind that these are low on the priority list. The popularity of this neck wear fastener has dramatically declined over the last few years and will probably die out completely in the near future. A major reason for this is because they can appear flashy at times and really aren't all that useful in non-windy conditions.