Crete? Plenty of less busy places to stay, a large island, plenty flights from Manchester, and lots to see/do. Also, southerly, so good weather more-or-less guaranteed in the autumn. I like Western Crete (flying to Chania, rather than Iraklion), there are a number of quieter places to stay in the West and South particularly. Chania is a lovely old Venetian town too.

Examples of some villas/houses
http://www.purecrete.com/
http://www.meonvillas.co.uk/villas/Greece/Crete/viewAll?x=23&y=5?rw.cm=google,ppc,crete+villa
http://www.crete-direct.com/

Lake Garda. Stunning scenery, nice warm weather in September and the crowds have gone. We had a fantastic stay in Limone, a lovely wee town, in a hotel with views of the lake.

How about Madeira? It's somewhere I'm waiting to go once my kids have grown up. It's just a bit further north than the Canary Islands and has lovely weather all year round. Very pretty scenery and some lovely quality hotels. Not sure about private villas there, but from what I have heard you will be very well treated and left to "do your own thing" (if that's what you want) in most hotels.

Bitez, in Turkey. We have been going for years (this will make 7) and we go from Manchester in September. Laid back resort but near to lots of history, nightlife and places to visit. No nightclubs, but plenty of restaurants and REALLY friendly people.

I would say Menorca,lots of places to visit and very easy to drive around.Roads are very quiet and there are lots of villas to rent or any other type of accommodation.We stay in the south at S'Algar where we have gone for many years but always travl round,I would'nt stay up the top end though i.e Cal'n forcat,Cal'n Blanes etc.The weather is also good in September.
Regards Mary.