if you just added a new kernel and did not remove the previous one,
then one easy way to recover is to put the SD on your PC, mount the
boot partition as well as the root FS partition and replace uImage and
uInitrd on the boot partition by the previous ones that are in the
root fs in /boot
if you did not remove the old kernel, the associated modules will
still be around in /lib/modules, so you should boot fine.
then you can remove the broken kernel with apt-get remove xxx command.