As has become a bit of a tradition - Google (UK) has changed their logo to reflect the day's celebration:
I noticed this this morning and thought - "How odd, they've left off the 'l' - the BIG L on Big L day". Well, The Register soon picked up on this too and even managed to get an official response on it - see that little green stalky bit? If you use your imagination and squint a little, you'll see it's the 'l'. Hmmmm.