Assuming comparing the 13" vs the 13"
Pro Only:
Firewire port
SD card slot
Backlit keyboard
Expandable to 8GB RAM
Standard 4GB RAM
Optional 2.66Ghz CPU
Optional SSD (as an OEM option)
Otherwise they're both C2D CPU, 250GB HDD standard, 320M GPU, etc.
The Pro is a tiny bit smaller too, but nothing that's a major factor.
A mini is basically the same architecture too (C2D 2.4 or 2.66, 320M)