Q-Park, Maxwell Street
Just behind the St. Enoch Centre, which blocks off your view to the north unless you're particularly excited about the St. Enoch Centre. To the east it's mostly car park. South, though, gets you up close and personal with the roof of St. Andrew's Cathedral, and it's also a great place to swatch the suspension bridge over the Clyde. The view to the west is amazingly cluttered, and takes in any number of bridges and buildings.
It's seven stories tall, I think. There is a lift.
Candleriggs Car Park
This one doesn't offer much but a view of the surrounding rooftops, but those rooftops are charming in their own way, many of them sprouting greenery. The north view is entirely blocked by a taller building, but you can see down into the alleyway where kitchen staff pop out for their fag breaks. To the west (if you're willing to climb the wall into a nook covered by a grating) you can get a good look at the boarded-up building opposite.
Again, seven or eight stories, and with a lift.
Oswald Street Car Park
The one you can access from Central Station. The view to the north and east is blocked by the roof of the station itself (it's incredibly tempting to climb on, they've made it really easy), but to the south you can see a fair way down into Tradeston, and to the west you can examine the Clyde Port Authority building's dome in profile.
Eleven floors, because they count each one seperately instead of using the a/b system. There's a lift, but I wouldn't trust it. You can get a little extra height by climbing the building which houses the lift mechanism, but it's not terribly worthwhile.
Buchanan Galleries Car Park
Adjacent to the, uh, Buchanan Galleries. Good, open views to the north and south, netting you Caley and the City Chambers, respectively. The easterly view is dominated by ugly tower blocks, and to the west you can see the miles of air-conditioning conduits that make shopping centres go. The walls are about seven feet high, mind, which is a bit of a pain.
Ten-ish floors, good lifts.
Cineworld, Renfrew Street
The viewing gallery on the top floor might've been designed to keep you a few feet away from the windows, which are slightly tinted, but you can make do. The view to the north and north-east is okay, but this one's mainly good for people watching. Or bus-watching, if that's your thing—you get a great view into Buchanan St. Bus Station.
Five floors (?), good lifts.
Tower, George Gilbert Scott Building, Glasgow University
Free daily tours (weather permitting), which start at 2pm and need to be booked a couple of hours in advance. Splendid views in all directions. Especially good from up here are Park Circus, Kelvingrove Museum and Art Gallery, and Kelvingrove Park in general. If the weather's really good you can even ascend the spire.
There is no lift. There are several hundred well-worn sandstone steps running in a tight spiral. In the dark.
I know they do them in Freshers' Week but I've always been busy. I'm going to have to go up some day it's nice 
. Although there is the slight problem the last time I tried to climb up a tower I got as far as the first landing, about 20 steps. That was in Bruges 7 years ago, and haven't climbed up a tower since (I did survive the CN Tower but I think lifts are different!).
