I'll toss in both the MOTU (Mark of the Unicorn) products. 2408 MKIII (I have the MK II version), and 828. both are very flexible and can even be used as standalone units. However, they are beasts. That is, they take up some room, they don't simply just fit into your computer (the 2408 uses a PCI card in addition to the external unit), so that can either be a negative or positive thing depending on your point of view.
Wayne
love the MOTU products.
we have the 828 and the 828mkii.
the standard 828 cant be run standalone, but the 828mkii can