That goes for me as well as Posie.

She's very good at "sit" (1 short peep) when she's next to me, "come here" recall (2 short peeps), "bring it back"/retrieve (3 short peeps), and quite recently picked up "find" (1 longer peep that rises at the end), but yesterday I tried again with the one I want as much as a solid recall - "stop" at distance. I waited until she stopped to check where I was from her usual 30-40m, then gave her the "sit" whistle. On 3 out of 4 attempts she gave an instant "sit & wait" to the point that I was able to walk all the way to her with a treat on show, or get her to only come once she got an "ok" or "come here" instruction.
What's so good about this is that we don't go out of our way to have training sessions, we mostly just fit them in with her walks. The number of neat little tricks that she's learned in a few attempts, and remembered thereafter, has come as quite a surprise given that we don't structure her training.
What does everybody else use for whistle commands? Is there a standard set?