There are loads of places... The most obvious and plentiful being the road that runs from outside the Glasgow Union through Kelvingrove Park (Kelvin Way I think?). The whole street, on both sides, is free all the time, and is about a mile long. Tends to fill up first thing though, you'll need to hunt after that.
There are other places, but it's taken me long enough to find them myself, and they're too small to give away... Sorry! The parking outside the uni front gate is pretty cheap, if you're going to be there for up to 4 hours, then you can park there (it is pay and display).