I wouldn't go 'writing' off the old CF yet! It still seems to be the cheapest per meg in the flash stakes. The easiest one to interface to would be the MMC (multimedia card) as it needs only 4 port pins to talk to it and you can use a butchered ISA edge connector from an old pc motherboard as a connector at a pinch! The code for talking to CF and MMC devices is pretty trivial apart from the filesystem.

It still seems to be a bit of work to have a small micro link the 8051 to talk to USB devices - you need a master USB interface i.c and a layer of software just to talk USB then you need the filesystem or a nifty way of storing the data.

If you are making 100 units - CF or MMC maybe the easiest and fastest route, if you're making 10,000 units then the USB route may be the way to go. There's plenty of USB dongles to read CF and MMC cards at cheap prices.