From Responsive Design[1] to jQuery Mobile[2] you really have a lot of options. Depending on your wants/needs you will find that each has its own benefits and downfalls.

There was also a good discussion recently about Responsive Design[3]

[1] - http://en.wikipedia.org/wiki/Responsive_web_design

[2] - http://jquerymobile.com/

[3] - http://news.ycombinator.com/item?id=4570193