Calista is lovely - I know a little boy who's Calisto.
I like Willa - after the author Willa Carter, but she'd be called willy.
Wallis after wallis simpson? nice enough, but she'll be called primark!
Topaz - semi precious stone, and exotic dancer - call her Jenna and be done with it!
Beryl is another name for Emerald, but is a bit Battle Of The Blitz. Ruby is lovely also if you want to stick to stones.
To me Cameron is one of those LA boys/girls/ androgynous names, camera-on. David Cameron might be next PM, would you really do that to a little girl though?
But then don't listen to me - we nearly called our DD Brunhilde, or Hildegard, in the end we didn't call her what we had decided upon: Solange - Sun Angel - as she didn't look like it at all, we opted for a more traditional French name, which suits her perfectly.
Good luck with the ttcing - friends of mine have had a boy after two girls - they opted for a very 'sedate' name for the boy after two lovely names for the older girls....