I think he is so unique (aesthetically and how he behaves on stage at least) that there are none really similar to him. Sonically, he's perhaps not quite as distinctive but he did have an effect and influence on a lot of the bands of the nu metal era. I remember quite a few players from that era who seemed to bring a bit of Flea's funky aggression to their style. They were perhaps the first generation of musicians in a big, new rock genre following RHCP becoming huge to really bear the influence of Flea's style.
Just go to a Guitar Center on any weekend. That’s where you’ll find the copy cats. As far as ‘in a similar style’, that’s entirely different.
I don't really hear many/any players where I think, "That sounds like Flea." I definitely hear players where I think, "That sounds like Larry Graham or Bootsy Collins," and without those two pioneers, I don't think we would be talking about Flea.
...if you like Flea- Muzz Skillings from Living Colour P-Nut from 311 Gang Of Four may be somebody you might like, too.
Futoshi Uehara from Maximum the Hormone. Awesome Band. J-Rock Metal. Played the Flea Bass and even has the same Tattoos as the Chili Peppers.
I agree with what's been said about Flea's uniqueness. Check out Norwood Fisher from Fishbone, and Rob Trujillo's playing in Infectious Grooves.