Most of the XMDF readers will do exactly what you're asking.
(1) The newer Sharp dictionaries i've seen do this. Specifically the Brain and Papyrus series. Example of the XMDF support for the newest models:
http://www.sharp.co.jp/edictionary/f...html#feature14
(2) Sharp also makes two versions of the Netwalker, a small form factor Linux palmtop. I have the new tablet and it comes with the XMDF reader, about 30 books and a lot of dictionaries - very nice. Details:
http://www.sharp.co.jp/netwalker/
Good stuff about the book reading feature:
http://www.sharp.co.jp/netwalker/pct...ook/index.html
(3) Most of the software installable readers that are available for XMDF have some kind of copy function. The key to this is having the dictionaries you're interested in. If you don't mind reading on the computer both Windows and OS X have very nice commercial dictionary support. OS X has some very good Japanese dictionaries built into the OS. Unfortunately no XMDF for Macs yet.
http://books.spacetown.ne.jp/sst/men...ead/kishu.html
(4) Sharp announced the new readers, but details surrounding their capabilities are sparse.
(5) You will be able to get a Zaurus MI-DC25 on Yahoo Auction with the book reader and dictionaries inside. I still have mine.
http://www.sharp.co.jp/products/mie25dc/index.html
(6) Many cellphones work. Including many from Docomo and Softbank but they are for the Japanese market - depending on the model will not work outside of Japan.
(7) Different Windows Mobile units from Sharp and HTC units from e-mobile also have reader support and good dictionaries.
http://www.sharp.co.jp/em/s01sh/
http://www.sharp.co.jp/d4/
And WinMo and PocketPC in general are supported.
(8) here is a 2chan thread about the format:
http://logsoku.com/thread/toki.2ch.n...lo/1231321170/
If you have specific questions about any of these please feel free to ask. I've probably owned or used most of the XMDF related devices available in the last 5-6 years. My current favorite is the Netwalker. However, the dictionaries can't be beat for instant on and instant word lookup. The screens are the trade-off.
Late addition: Somewhat dated model capability chart by type:
http://books.spacetown.ne.jp/sst/ven...lchart.asp#mav