Flying visit to Scotland - Glasgow area

Stirling if you like magnificent castles and a number of interesting spots on the way - less than an hours drive

Edinburgh is only about an hour away

Loch Lomond and the national park is close by - about an hour or so I think - beautiful countryside http://www.lochlomond-trossachs.org/

The roads are fine. Accomodation is similar to the rest of the UK and there is a wide range of options, from youth hostels to 5-star hotels.

Or you could do an overnight trip to the Isle of Arran - involves a ferry ride, you can take the car

I wouldn't go over to Arran if you're only here for a couple of days. The ferry is pricey with a car, and there are lots of good things nearer the city.

Take a drive out to the Drovers Inn at Inverarnan for lunch. Not so much for the food, which is pub grub, but for the drive, and the decor. It's about an hour north of Glasgow, and the road takes you right up Loch Lomond side. You can stop at Balloch, (there's an aquarium at Lomond Shores) or various other places for a walk, or maybe do a few miles of the West Highland Way, if you've got boots and the weather is nice.

If driving is more your thing than walking, carry on up the A82 to Crianlarich, then loop back to Glasgow on the A84 through Callander (great Tea rooms) and Aberfoyle. All in all it's about a 3 hour round trip, but you'll see some gorgeous scenery, and pass through some nice wee towns.

Loch Lomond is an ideal spot for a visit from Glasgow. Whilst you're in Glasgow, if you like parks and greenery you can check out Pollok Park in the south side of the city, it's a huge big country park that's also got a museum - the Burrell Collection, a stately home - Pollok House and Highland cows are kept in fields in the park.
You could also visit the Botanic Gardens in the West End, take a walk down Byres Rd, stopping for lunch in one of the many cafes, then mooch along past Glasgow University (it's worth a tour) and then through kelvingrove Park to the kelvingrove museum.
Hope you get sunshine!

Thank you all for your suggestions - we went to Loch Lomond in the end, stayed by Loch Long, was very chilly but very pretty! Stopped by Balloch at the south end of the lake on our way back.
Thanks again!