• Carolingian Polyptyques at the University of Leicester
• " Polyptyques are inventories that list the human and physical resources of great landed estates, especially monasteries. " (Hang on to that word for playing Scrabble! :P ) 
• Disocorides, De Materia Medica
• Multiple PDFs published by http://www.ibidispress.scriptmania.com
• Tacuinum Sanitatis
• The extant copies are believed to have been made in Lombardy, yay!
• Copies of the illuminations at GodeCookery.com
• The full text is probably somewhere online, I just haven't found it yet ...

The Biodiversity Library has a wonderful site that provides historical info on spices. It does link to primary texts, but unfortunately the pre-1600 ones will probably not be in English.