DS1 goes to Heritage House on Albert Drive and I'd recommend it. It's part of the Careshare group, and in one of the big sandstone villas in the leafy bit of Pollokshields. They have lots of outdoor space (which seems to be a problem in lots of the places that I saw). The staff are lovely and the whole atmosphere is good.
Other places in the area:
Hyde n Seek in Prospecthill Road (just next to where they're building the new hospital). We visited this and liked it too when we were looking.
Daytime Playtime in Bolivar Terrace. I think this may have changed names recently. DS1 went here for about a month, but I didn't really like it and we were lucky enough to get a place for him at HH at short notice so all worked out.
Poppins on Queen's Drive. I'd heard good things about this place, but one of my friends withdrew her son from it as she wasn't happy and neitehr was he. He's now at Rainbow pre-school also on Queen's Drive, which he loves. It's Christian, though, so it obviously might not be suitable for some people. And it's pre-school only.
There's also a small pre-school nursery on Regent Park Square (not sure of the name) - I think they only take children who are potty trained so not for littlies.
HTH if you haven't found somewhere already.