Basic or Pseudo Basic languages: 

A family of visual software tools that enable development of GUI applications for non-PC computer products. Works with MS Visual Basic.

Like the name says... nice and simple. A VB-like environment for coding Palm OS applications. NSBasic also has toolkits for Newton and Windows CE development.

A full-featured IDE that employs a basic-like syntax for writing Palm OS applications. Allows you to visually-design and edit Palm Databases.

Java Tools: 

The Connected Limited Device Configuration. Allows you to code for the Palm OS using Java.

The Mobile Information Device Profile for Java. Targets cell phones and pagers.

The kAWT project is an implementation of the Java Abstract Window Toolkit for resource constrained devices. There are implentations for both PDAs and cell phones (MIDP).

A sophisticated development environment that allows embedded device programming in Java. Uses the IBM J9 virtual machine technology.

An SDK based on the Java MIDP for programming the Motorola IDEN phones, the first phone with Java 2 Micro Edition support.

A Java based API for Palm OS, IPaq, Newton, and Windows CE.

A library for use with the IBM Visual Age Micro Edition that has many convenient hooks into the Palm OS API.

Program RIM devices in Java. Proprietary API at this point, but will support the Java MID Profile in the future.

API and toolkit using the Java MIDP for cell phone and pager programming.

C/C++ Tools: 

C/C++ IDE for Palm OS programming

For RIM devices uses C/C++

A C-like language for developing Palm OS applications. Comes with a nice IDE.

PRC-Tools is a complete compiler tool chain for building Palm OS® applications in C or C++.

C/C++ IDE for Palm OS programming.

WAP Tools: 

Requires registration as a Nokia developer, but has lots of other tools as well.

Requires registration as an Ericsson developer, but has other tools for download.

Other languages/proprietary:  

Allows you to author HTML content that can be displayed through a web-enabled Palm device.

Uses the Forth language and features an on-device compiler. The IDE itself runs on the device. Hope you are a master of grafitti...

Pendragon Forms is a fast and simple way to create data collection applications and conduits

Utilities:  

Allows you to test your applications without downloading to the device.

Tool which will convert a csv file into a Palm Database, and vice versa.

SyncML is an XML implementation that attempts to have a common format for data synchronizaiton across many devices and platforms.

Enables developers to perform development and QA testing of their WAP Clients and Gateways.