I've always been really into Wassel peanut tanks or maybe a skinny Sporty tank. I like some of the molded tanks as well.
Some guys are always pushing different lines on their bikes. Check out this tank from http://daikoube.blogspot.com/, tall, skinny and ribbed. I'm torn, not sure about it. Looks like it was executed nicely and the paint looks awesome, great design. Who knows, just watch, I'll have one next time.