We keep an updated list of Ultrabook alternatives here.
Apart from the Apple MacBook Air which is built like an Ultrabook but sold like an Apple product, there are other interesting options that hover just outside the weight and features list of a true Ultrabook. You’ve got options with Core i3 or AMD E450 at way below the Ultrabook price level, options without SSD and even high-end options. If you can handle just 500 gm / 1lb more weight and are flexible on specs you can save hundreds. In this report I list your options for Sept-Oct 2011.
Before you take a look at the Ultrabook alternatives, have a look at these two reference articles to find out exactly what an Ultrabook is.
Backgrounder: What’s an Ultrabook?
Backgrounder: Ultrabook features Guide.