Around 5 years ago I built a simple sparkline generation script in PHP. It wasn't very good, the lines were shaky even with antialias. During last weekend I thought I'd rebuild it from scratch to see how much better it would be second time around.
A few hours later and it was complete, the lines were thick, antialiased and almost identical in quality to the Google Image Charts version. I also added browser caching using the ETag header.
The key bit of logic that I failed to think of 5 years ago was to create the original sparkline larger than the desired size, then scale down by the same factor. The resizing naturally makes the lines smoother than imageantialias and imagesetthickness ever could.
It's as easy as this to use:
<img src='sparkline.php?size=80x20&data=2,4,5,6,10,7,8,5,7,7,11,8,6,9,11,9,13,14,12,16&back=fff&line=5bb763&fill=d5f7d8' />