HandyShopper is a great shopping list tool, with plenty of features. You can even use it for other kinds of lists! HandyShopper works on Palm OS v2.0 through v4.0, on all Palm-based devices (including HandSpring, Sony, HandEra, etc). Visit the HandyShopper User Group to get or share ideas, etc.
And best of all, HandyShopper is FREEWARE! Update Description:
HandyShopper v2.9c, build 7908 (7/8/2005):

• The Databases screen now lists databases from all cards and internal drives.
• Detect Zire31 two-button devices and adjust the one-handed mode controls accordingly.
• Fixed the direction pad when editing a field in the main list view.
• Fixed the popup calculator after a Lookup takes long enough to show the progress indicator.
• Support for the T5 and Treo 650 direction pads.
• Other minor features and fixes.
• See the enclosed HISTORY.HTM for details.

HandyShopper v2.9b, build 6802 (8/2/2004):

• Fixed miscellaneous minor issues.
• See the enclosed HISTORY.HTM for details.

HandyShopper v2.9a, build 6715 (7/15/2004):

• The Lookup filter is more responsive to Graffiti in large databases or on slow devices.
• Fixed miscellaneous minor issues.
• See the enclosed HISTORY.HTM for details.

HandyShopper v2.9, build 6512 (5/12/2004):

• New and improved Lookup that filters as you write.
• Freeform text Aisle fields.
• Many other new features and fixes; see the enclosed HISTORY.HTM for details.

HandyShopper v2.8c, build 6119 (1/19/2004):

• Fixed potential crash caused by how Agendus 7 modifies your existing icon sets.
• Detect both the "Zire" and the "Zire 21" devices and enable one-handed mode to work on both devices with only two buttons.
• Worked around minor OS bugs in the Treo 600 direction pad, and the Handera 330 'Scale to fit' mode.
• Fixed some obscure bugs.
• See the enclosed HISTORY.HTM for details

HandyShopper v2.8b, build 6013 (12/13/2003):

• Fixed a scrolling bug in the list view.
• Fixed crash on Tungsten T3 devices when choosing a date in the list view.
• Fixed the list of databases which could sometimes forget about an expansion card.

HandyShopper v2.8a, build 5903 (11/3/2003):

• Added support for devices with a collapsible Graffiti area (for example devices with a 320x480 screen). Any Palm OS 5.3 or higher device with a collapsible Graffiti area is supported, regardless of the screen resolution or size. Sony Clie devices with a collapsible Graffiti area also supported. Tungsten T3 devices are supported, but require installing some patch files (see the top of the enclosed FAQ.HTM file for more information). The collapsible Graffiti area on other devices is not supported, and HandyShopper will behave as if the device has a normal Graffiti area.
• One-handed mode supports more devices: Palm Zire, Treo 600, and Kyocera 6035 (see enclosed HISTORY.HTM file for details).
  
• Tap+hold in the Quantity field skips the popup list and lets you edit the field directly without having to choose 'Other' from the popup list.
  
• Various fixes, especially some problems in the Edit Categories screen, particularly on devices with Palm OS 3.3 or lower.
  
• See the enclosed HISTORY.HTM for details, or the enclosed FAQ.HTM for answers to frequently asked questions, or the enclosed README.HTM for general information and how to get started.

HandyShopper v2.8, build 5530 (7/30/2003):

• Bluetooth support.
• Graffiti works in the Units popup list.
• The Checkout command is included on the popup actions menu.
• Added customizable icons for categories.
• Added a small font for high resolution OS 5.x devices. Sony OS 5.x devices can use the small font, but not Sony OS 4.x devices cannot.
• Several fixes.