Bitstream Inc. has released ThunderHawk 2.1 Pocket PC Edition with full Java support. Apparently, ThunderHawk 2.1 offers desktop-level Java 1.5.0 capabilities, allowing Java applets to behave exactly as they would on a desktop browser.
I say apparently because a thread on Pocket PC Thoughts indicates that the Java implementation is entirely server-side, thereby limiting its usefulness.
ThunderHawk works on a subscription basis with both monthly subscriptions ($5.95 USD per month) or annual ones ($49.95 USD). A trial version is available and the upgrade is free for current ThunderHawk users.