The canvas approach suggested by Amaan is definitely today's approach to generating images client-side.
In the past, the most common solution was to use a library like Cufon. From the Cufon wiki page on its usage comes this snippet:
Cufon generates the client-side version of the font up-front. This means it just adds static files on your web server, instead of generating the images on the web server (like with ImageMagick).
