I was thinking about a GuruServer Plus because of the uSD support, where I could even store larger applications and files, such as OpenOffice, if it's not too heavy for its CPU.
The SheevaPlug also has Support for SDHC-cards, so storing some data isnt a problem with a 8 oer 16GB SDHC-Card.
And the SheevaPlug hasnt the problem with the heat....only sometimes the (changeable) power-supply.
If you dont need WLAN or GBit-Ethernet you could buy a SheevaPlug or SheevaPlug with eSATA