Long seatposts.
Large/Small frames (17" is usually about perfect, and conveniently, my size)
Full Suspension, except for the GT STS style which I have a soft spot for.
Bling. Any coloured anodised parts just look pretentious and detract from a beautiful bike
slicks/small tyres. Something around 2.1" looks just right IMHO, but I appreciate the need for slicks and smaller tyres to suit conditions. This thread is about looks though, not practicality.
Kleins. Just don't like the look of them.
Some older frame designs with tall head tubes or LONG flat top tubes.
That's enough for now.