I second MobiSystems dictionaries, they're great - I use the Spanish/English one myself. A tad expensive but I am very pleased with the product and support I have received. The dictionary files themselves are big and are stored on your SD card (if you have one), it can use many dictionaries at one time (you switch with a simple menu click), and they even support online dictionaries. You can even mix-n-match registered (paid for) dictionaries and trial dictionaries at the same time.