Alan: I look like the character, I'm not actually him.
And of course, when Daniel Radcliffe guest-starred, they made the whole episode about "Hocus-Pocus" and made quite a few references to Harry Potter. As Daniel had apparently done some research into real-life tricks and the history thereof, the net effect was to rig the game in Radcliffe's favor.
Radcliffe's buzzer was a clip of him shouting "Expelliarmus!"
On the other hand, he got some Potter trivia wrong; on being questioned about the rules of Quidditch, he stated that capturing the Golden Snitch automatically won the game for the catcher's team, which is not true. (Catching the Snitch ends the game, and gives the catcher's team 150 points, so the net effect is usually a win, but there is at least one canonical example of the catcher's team losing.)
Also a bonus for Alan Davies, who was able to put his aforementioned "experience" as a magician's assistant to good use.
A Never Mind the Buzzcocks-style identity parade occurred when Phill Jupitus was on the panel in the episode "Indecision".
Whenever Jeremy Clarkson is on the programme, expect at least one reference to or question about cars and motor vehicles, if not a direct reference to Top Gear itself.
In "Ice", Brian Blessed's first appearance, Sean Lock appropriates Blessed's most famous line from Flash Gordon.
In "Immortal Bard", the Shakespeare episode, a question on Lord Byron leads to Stephen referencing a joke he once used in a monologue called 'The Letter' for Footlights Revue.
Stephen: He had from birth a pronounced limp. L-I-M-P, pronounced 'limp'.
In "Jingle Bells", when Stephen brings out a jingling johnny:
Phill Jupitus: You were supposed to not bring any props from The Hobbit back!
In the 11th series episode "K-Folk", Stephen mentioned that he didn't get an invitation to Alan's wedding:
Alan: I did invite you, but you were abroad! You were filming an episode of Bones!
A double example for Jeremy Clarkson and Jimmy Carr in "Kings":
Jeremy: Red diesel for farmers, which you aren't allowed to put in your car, and I don't. (aside glance at audience) Jimmy: Evading tax, Jeremy. It's a slippery slope.
A Producer's Allusion took place in Season D Episode 4; when discussing the village of Didcot, Stephen commented that a Didcot is in fact, "the tiny oddly-shaped bit of card which a ticket inspector cuts out of a ticket with his clipper for no apparent reason. It is a little-known fact that the confetti at Princess Margaret's wedding was made up of thousands of didcots collected by inspectors on the Royal Train." He then commented that this was not actually a fact, but a quote from The Meaning of Liff, co-written by QI producer David Lloyd and Douglas Adams. Lloyd slipped the "fact" on Stephen's teleprompter.
During "Kris Kringle", a football originally smuggled into the trenches for one of the Christmas truces of World War I was presented to Stephen by a soldier named Tony Robinson. He is indeed nicknamed Baldrick, and Blackadder references ensued, including the requisite baaing.
Also during "Kris Kringle", Brendan O'Carroll wore a jumper which had Santa's body but not head on it (making it look like Santa had O'Carroll's head). The Christmas Special of Mrs. Brown's Boys (which O'Carroll is best known for, and which aired a few days before "Kris Kringle") featured the same Visual Pun with Grandad and Baby Jesus.
Of course there would be references to Star Wars during Carrie Fisher's appearance in "No-L".
Missing Episode: The episode "Idleness" was in limbo because the week before its broadcast panellist Jeremy Clarkson made controversial comments on The One Show about strikers that led to over 30,000 complaints. It was, however, accidentally uploaded to the iPlayer, and somebody managed to get it on YouTube before the BBC realised their mistake. It ultimately aired in May 2012, one week after the Shakespeare special.
No Export for You: The cost of clearing the rear-projected images for international showing has put paid to no fewer than four attempts to bring the programme stateside. However, Series F has been broadcast in New Zealand, and Australia broadcast Series F and G, then looped back to Series A - E before resuming with Series H. Also, the show has been remade for the Dutch market at least; the host of the Dutch version made a guest appearance during Series G to demonstrate the correct pronunciation of "van Gogh".