I use my 6" straight more than anything. But it has been discontinued by the manufacturer. Many Template manufacturers make a simple 6" straight with laser etched reference markings at 1/4 increments.
Next I use circle templates. Again mine have been discontinued but Handiquilter makes some nice ones. I like them to be marked at 45 degree intervals and again have half the circle marked with 1/4" spacing lines. Be advised that most manufactureres that sell circles do not account for the 1/4 hopping foot. So circles marketed at 2" for example, will quilt out at 2 1/2". There are some that the template accounts for and you will quilt out a true 2" circle (the template will only measure 1 1/2"
Next I use Rhonda's crescent (medium but I have the small and large too) and S rulers (I have medium and small) for curved cross hatching.
You can get rulers from a few different suppliers. The prices are usually the same. I like Quilters Rule and Erica's
These are the basics that I turn to regularly.