I just read a handy tip from Kate Morrical's blog (from 2009......yes, 3 years ago), LT Unlimited, about how to create circles when you are drawing in isometric views. You can use the Elipse command and type i (for Isocircle). You specify the center of the circle and it defaults to a radius or you can switch to diamter (just like a regular circle). Presto, a circle in an isometric view! I'm not sure how long this feature has been around, but WOW, what a handy tool.
I created a couple of buttons to toggle between standard and ismetric snap grid styles (for rectangular and isometric respectively):
Also, you can toggle between isometric views using the F5 key on your keyboard for isoplanes top, left, and right.
I subscribed to Kate's blog today as I'm sure I've missing several helpful tips (http://ltunlimited.typepad.com/). I hope you all find these things as handy as I have! Check out Dean's blog while you are at it - the dude knows his CAD (http://ltisacad.blogspot.com/)!!
I use this macro to toggle the snap style. System variables and diesel are really nice!
For me it's worth it to find a way to toggle instead of taking up screen space with two buttons.