2405FPW, 2407WFP, 2407WFP-HC, 2707WFP, 3007WFP, 3007WFP-HC
MicroDrive: 340MB - 1GB
SmartMedia: 8MB - 128MB
Media Stick: 8MB - 128MB
MMC: 32MB - 128MB
SD (Secure Digital): 16MB - 512MB
SDHC (Secure Digital High Capacity): None

2408WFP, U2410, 2709W, 3008WFP
CF Compact Flash 2.0: 128GB
MS  Stick 1.40-00: 128MB
MS Stick 1.43: 128MB (U2410)
MSPRO Stick 1.01-01: 32GB
MSDuo Stick 1.10-00: 128MB/32GB
xD  Picture Card 1.2: 2GB 
SD/SDHC Memory Card 2.0: 32GB 
MMC MultiMedia Card 4.2: 32GB

Other cards might work but Dell cannot support them.