The Horse shoe is a must if you like an old traditional pub with character, its cheap and cheerful with no frills......you could encounter the odd Jaikey to add to the atmosphere.
The Counting House on George Square as mentioned by Ralphie is OK but a typical pub chain. As Mick says there are plenty pubs in and around George Square including poncy wine bars and real ale
The Waterloo seems to be a favourite of Dazza....but could be a pain in the arse.
Try looking at this list but not all Glasgow pubs are on it,
http://www.glasgowguide.co.uk/pubs.html The best way is just wander about as you will find dozens all within walking distance of your accommodation, and you will be ok if you stay within the city centre.