My DS2 has was at Union Grove Community Day Nursery for a year. It's on Union Road which is just on the border btw SW4 and SW8.
There have a beautiful new building on Union Road, which offers full time places only, at £155 a week for under twos. Very very cheap for the area - they are a charity. They also have a dark shabby old building around the corner which offers part time places. DS2 was actually only there 3 or 4 days a week but we paid the £155 to get the nicer building because the difference was so huge.
I wouldn't say it is absolutely perfect (hence we moved DS2 once he was old enough for the very lovely Pelican Montessori in Kennington) but it's definitely a good nursery and imo better than most of the privately run operations in the area.
Personally I would give Magic Roundabout a wide berth. When I was looking into nurseries there were something like 13 complaints which had been upheld against them listed on the ofsted website. I think they aren't listed any more (as they've been superceded by a more recent inspection) but they were for really basic and worrying stuff like staff not being CRB checked and the front door not being secure. I'd also have more general worries about the size of the place. They are registered for something like 180 children. If your toddler wandered into the wrong room, would the staff in there know their name? Having said all of that, my views are mainly based on hearsay and are out of date so I wouldn't take them as gospel.
I've also heard St Michael's is lovely but it's a pre-school so only for potty trained over twos and not full day care - school hours only.
Finally, I believe quite strongly that there is nothing better than a good childminder. We had a wonderful childminder for DS1. I loved him being in a home environment, and the way that his daily routine was a normal family life, not an institutional regime. But you do have to find someone you really really trust, which we didn't manage second time around, hence the nursery.
One more thing (definitely the final thing!) - I know you're trying to get organised but it's very hard to know what you want before you've had the baby. I don't think you can really tell in advance what will be important to you. And different children suit different environments. It's good to know what the options are (and what they cost) but best not to comit too early if you can avoid it.