As some of you might have guessed, I'm a big fan of Asimov's Robot stories and novels. I'll try to offer any insights I can.
I would recommended The Complete Robot if you're looking for more Robot short stories. It contains thirty-one robotic tales, but you should be aware that nine of them are the same stories found in I, Robot. How much you're willing to double-dip is up to you. Of course, that's still not all of the Robot stories, but it's a pretty good sampling, I think.
Some of the stories clearly don't exist within the same Robot/Empire/Foundation universe that the others do (most notably "Victory Unintentional" and "Let's Get Together"), but you can just treat them as taking place in an alternate universe.
There's also one story --"Mirror Image"-- that takes place between the Robot novels The Naked Sun and The Robots of Dawn, and features the primary characters of those books. The rest of the same-universe stories take place before the first novel, The Caves of Steel, so I'd suggest reading them first.
If you want to go even further, The Early Asimov, a collection of Asimov's early short stories, contains one entry called "Mother Earth". It doesn't deal with robots, but it does somewhat bridge the gap between the Robot short stories and novels (even if some of the predictions made in the story don't actually come true in the Robot novels -- I guess Asimov changed his mind about them). The other stories in this collection are unrelated, and some are a mixed bag, but you might find them worthwhile if you're looking to broaden your exploration of Asimov.