I love the idea of having custom cake toppers made to truley represent the bride and groom...and no one that I've seen does it better than HellinaHandbag. I found her on etsy while searching for off beat wedding ideas, and I just love them, it is exactly what I would want on my own wedding cake. She takes vintage cake toppers and re-vamps them with your style, hair color, dress details, and even your tattoos and makeup! Prices range from $50 - $150. Visit http://www.hellinahandbag.net and click on "custom orders" for ordering information.
Another idea I came across for all you Steampunk guys and gals are these really awesome robot cake toppers by The Builder's Studio on Esty.com. They start at about $100 an go up from there.
