Note: Steve's a Pocket PC fan and writes from that perspective. But almost all of his advice also applies to the Handheld PC.
The Windows Powered Pocket PC is like a portable toolbox, containing the things you need to get work done (and have a little fun). Certain
tools are built into the Pocket PC, including Pocket Outlook, Word, Excel,
Microsoft Money, MS Reader and more. And if you don't find the tool you need, you can add it later on, selecting from a growing number of software
applications available from independent developers.
Pocket PCs also ship with the basic hardware tools you need, including the touch-screen stylus, connectivity cable and/or data cradle, and in
some cases a slip cover or carrying case. As with software, there are many more hardware accessories available to help you customize your Pocket PC.
Most Pocket PCs and all Handheld PCs come with an industry standard Compact-Flash (CF) expansion slot built in. The Palmax Amigo Pocket PC
has the larger PC Card slot. A CF or PC Card slot can be added to the Compaq iPAQ via an optional Expansion Pack. Only one Pocket PC, the Cassiopeia EM-500, is equipped with the smaller MultiMedia card slot, which can be used to add storage memory only. The CF and PC Card slots on the other devices make it possible to select from an increasing number of industry-standard hardware accessories to enhance the capabilities of the Pocket PCs.
The rest of this article is my take on the top 10 "must have" hardware accessories for the Pocket PC. These are not in any particular order. Some of these slip into the card slots I mentioned above. Others don't have anything to do with the slot. They all add significant capability to Pocket PCs.
Storage cards add file storage for music, video and more
The Pocket PC is not only a workhorse; it's a portable entertainment center with eBook, music, and video capability. In addition, there are many exciting games you can download and install. However, these things can quickly fill up your Pocket PC's limited file storage space. This is especially true with music and video files, which can be very large. One of the best accessories you can get for your Pocket PC is a storage card.

Storage cards come in three physical sizes. The largest is the PC card (left), about the size of a thick credit card. The CompactFlash card (right) is about 1/3 the size of the PC card. The MultiMedia card (bottom) is about the size of a small postage stamp.
Storage cards come in three physical sizes: MultiMedia card (smallest, used with the Cassiopeia EM-500), CompactFlash card (for most other Pocket PCs), and PC card (also referred to as a "PCMCIA" card; for most Handheld
PCs but can also be used with the Palmax Amigo and Compaq iPAQ). Many
manufacturers produce storage cards in these different formats. Check out
SanDisk (www.sandisk.com),
Pretec (www.pretec.com), Kingston Technologies (www.kingston.com).
The storage capacities of these cards range up to 64 Mb for the MultiMedia
cards, 320 Mb for the CompactFlash cards, and 1.2 Gb for the PC cards. Also, IBM manufactures a high-capacity rotating disk "microdrive" in the Type II CompactFlash format (www.storage.ibm.com/hardsoft/diskdrdl/micro). IBM microdrives come with capacities from 340 Mb to 1 Gb. These can be used in the Type II CF slots of Cassiopeia E-115/125 Pocket PCs and the iPAQ (via its optional CF Expansion Pack). It can also be used in any Type II PC card slot with the help of a CF-to-PC card adapter. This means that it can be used with Palmax Amigo's PC Card slot or the iPAQ's PC Card Expansion Pack. Kingston Tech-nologies
manufactures a 2 Gb rotating disk hard drive similar to the IBM microdrive, but in the larger PC card format.
CompactFlash "landline" modems connect to the Internet