Hambleden (Bucks.)
Also featured in several Midsomer Murders episodes, most notably Blod Will Out (the church, post office and stores, and Stag and Huntsman pub); the pub also in Who Killed Cock Robin?, Down Among the Dean Men, and The Glitch.
Hurley (Berks.)
The cloisters and refectory next to the church were used as Dr. Clive Warnford's house in Blue Herrings.
Joyce buys charcoal at the village shop in Midsomer Life.
Ye Olde Bell Hotel became the Magna Hotel in They Seek Him Here.
Bledlow (Bucks.)
The Lions at Bledlow pub appears in multiple episodes under a variety of names, including in Dead Men's Eleven, King's Crystal, Blue Herrings, Dark Autumn, and The House in the Woods.
The Bledlow village church appears in Death's Shadow and Worm in the Bud.
Chenies Manor (Bucks.)
Edward Allardice's home in Judgement Day, Aspern Hall Museum in Beyond the Grave, and Malham Manor in Orchis Fatalis.
Watlington (Oxfordshire)
The town hall and several shops in the High Street can be seen in Judgement Day.
The Watlington Branch Library (near the war memorial), redesignated as Causton library, appears in the background of a meeting between Scott and Cully at "Midsomer Travel" in Orchis Fatalis.
Watlington church was used in Ring Out Your Dead.
According to one of my guides, "a lane leading off High Street" became Lower Warden in A Tale of Two Hamlets. Despite the scruffing up in the episode, I'm reasonably sure that this is it (albeit from slightly different perspectives), but in case it isn't, let's go with this one as a stand-in, shall we?
Long Crendon (Bucks.)
Another perpetual favorite of the Midsomer Murders production crew with multiple appearances throughout the series (and more being planned for the future), including:
The High Street, all the way downwards from the church and courthouse at the upper end (see first 3 photos). was used for part of the "Oak Apple Day" celebrations in Dead Letters, and also as a street setting in Death and Dreams; in addition, a number of individual cottages have been used as character residences in other episodes.
Never mind the use of a building in Watlington as Causton Library in Orchis Fatalis (see above), in Dead Letters the honors go to the Long Crendon library! (The interior -- unfortunately closed when I was visiting -- can be seen in Blood Wedding.)
The Eight Bells pub makes an appearance in A Tale of Two Hamlets.
Westington (Bucks.)
A well was brought to the Westington village green as a prop for a body to be found in it in the episode Who Killed Cock Robin?, and to the extent that the "Oak Apple Day" celebrations in Dead Letters didn't take place in Long Crendon (see above), they were filmed here, too.
Dinton (Bucks.)
Dinton church was used for the wedding at the end of Who Killed Cock Robin?
Chinnor (Oxfordshire)
The Chinnor terminus of the historic Chinnor & Princes Risborough Railway became Holm Lane Junction in Death in a Chocolate Box.