I have been to lunch at Simpson's twice - I think their Saturday lunch is excellent value. I believe it's £30 for 3 courses, and everything has always been great. In my experience, you can get lunch reservations with just a couple of days notice, and it's easy to reserve via their website.
Haven't been to Purnell's (going in Aug) or to Turner's yet. My partner had a work dinner at Cielo and said is was very good as well.
I also really enjoy Lasan, a modern India place in the Jewellery Quarter. The Island Bar is scruffy, but makes fab cocktails (no food though).
B'ham is packed with the UK chains - I think independents aren't really out in force here yet. Sometimes it can feel like there's Pizza Express or Simpson's - not much in the middle