<p>Can anyone recommend a library for chart generation (bar charts, pie charts etc.) which runs on both Java and .Net?</p>

Have you looking into using
JFreeChart
.
I have used it on a few Java projects and its very configurable. Its free but I think you can purchase the developers guide for $50. Its good for quick simple charts too. However performance for real-time data is not quite up to par (Check out the
FAQ
).
They also have a port to
.NET
however I have never used it.
Hope that helps.