I'd like to log data, perhaps 150k-250k with an Arduino. Using an SD card is a bit overkill. What could I use instead?
How do you plan to get the data out of the Arduino after it is logged? The SD card is super-useful for that reason alone.
Look into FRAM memories. Or any kind of I2C memory chip.
Im using it as bank for static data for webpage. Small sized board. Tested for 400khz -ok.
Addresses are predefined on this board so u need to modify schematic if you are not comfortable with the range 0x50 up to 0x53
Plan to tweak the traces for 1mhz when will have time.
Flash memory chips can work, too.
Indeed you have to find a way of getting your data off of the Arduino, assuming you're logging for external use.
I prefer sending the data to a remote server. Then you can make all kinds of great web interfaces using the data and connect it easily with all the other data you've collected from all your other microcontrollers.
Then use an esp8266 and log using its built in flash.