Miles of Exotics, 345 NW Barry Rd (North KC)-- This is the best
LPS I have found so far in KC. Helpful and friendly staff and an excellent selection of fish. Also, they carry Bio-Spira! If you like birds and/or reptiles, they've got that covered as well.
4 1/2 (out of 5) stars! I'd give them 5 stars, but size constraints keep them from stocking a good selection of aquariums.
Brothers Pets, 4015 Sterling at I-70 and Sterling--Excellent selection of fish and aquariums. They're quite popular it seems and sometimes service is slow, but overall generally good. The knowledge of some of the staff is sometimes spotty, but the owners know their stuff. They don't carry Bio-Spira though so that costs them half a star.
4 stars.