If you want to keep it classic : Valve Hammer Editor 3.5 with Floating Point fix
If you want to keep up with time : Sledge editor or Jackhammer editor
Sledge is developed by our beloved Pengy san.
FGD for Half Life : Classic half life FGD
FGD for Counter Strike : Hex 805 FGD
Best compuile tools : VulzaCN HL Tools (VHLT) V34
You can get all that, and more, here: https://sites.google.com/site/gshltools/
There are also Half Life FGD improvements, but I haven't got into that much. You can read more here: http://www.flat2d.com/hammer.aspx