Saw that I had ext3 running on some of my SSDs which supposedly does Not support TRIM. Time to convert them to ext4!

umount /dev/sdb1
fsck.ext3 -pf /dev/sdb1
tune2fs -O extents,uninit_bg,dir_index /dev/sdb1
fsck.ext4 -yfD /dev/sdb1

Then change the mount options in /etc/fstab:

/dev/sdb1    /mnt/sdb    ext4    defaults,noatime,discard,nodiratime,errors=remount-ro    0 1

All done! Now let the TRIM-ing begin! :)