Tis a tough call Steve but for a no. of reasons:

1) My darned left foot has developed some additional nasty pains and I suspect the writing's on the wall here so a move to a tip (most likely) or a lighter clutch on a non 'S' (I've driven a cpl and they're a touch lighter) makes sense
2) We'll be moving house next year and need a bit of extra cash (or a job lol)
3) My house resembles a car park so selling the Cayman and convertible beamer makes sense (3 cars and one garage = man maths)
4) Boxster gives me back the soft top (a must have somewhere)
5) The Cayman always was a luxury I couldn't afford to have for too long
6) When the Cayman was away for months I got 'car-bored' and bought the beamer. Still like it but 3 no longer makes sense.

I won't be doing anything in a hurry that's for sure - it has to be right or not at all.

It looks likely that I'll be hunting for a good Boxster - and would love some thoughts on how to find a good one - I'm in no hurry.

It could be an older high mileage one provided it's already had a good rebuild. Heated seats are a must and it could be a 986 (but with glass rear window) or a 987. If it's an 'S' it'll have to be a tip otherwise tip or manual (happy with the smaller engine - especially if they have fewer issues?).
Why will it have had a rebuild? Maybe IF it had IMS or Bore score issues, otherwise maybe not. There are cars that have gone to 150-200K on original engines.
Not sure on heated seats, never felt the need, the heater is vocanic! Mine is a 986 with a glass window, BUT be careful, the window is quite small & visibility is err.... pants. e.g. I frequently put the hood down to reverse.

What should I look out for, what should I avoid - no lemons for me thanks!
BIG issues are condensers & radiators. They crud up with a salt damped mulch & die. Around £600 for the bits plus labour. RMS weep, all seem misty, on a Tip no clutch to change so will have to be Tip box out not cheap, mine will be left.
Suspension is variable, the various bits are now available on the after market cheaper than OPC but may need changing as the miles go up.
Mine has had a tip fluid change, around £320 at an OPC but made a vast change to the gearchange quality.

Does anyone know of a good one anywhere?
Loads about, be picky about history & spec, on a 986 the options were expensive, mine was a £43K with £9K of options on!
Some were significant some not.
Worth a look on Boxa.net always a few cars for sale there.

If I find a good one my Cayman will be up for grabs - if not I'll stick until I do.

Any thoughts appreciated