I took my dd to the cutest class last week in Hampstead. It's called Mini Ps and it's a music, movement and make believe class for toddlers. My dd loved it and the teacher was brilliant. We sang (or listened) to great and apparently home spun songs all about Under the Sea. It's a bit more expensive than Monkey Music, but SO much better. We've also tried Gymboree but that seemed really tired.
They do a free taster class, if you near then do go and try it.