what kind of light to you have on your 90 gallon tank? if under 3 watts per gallon, i would suggest, as you stated, mushrooms.. possibly some zoanthids.. anemones need strong lighting and very good water quality. if you have 3 watts or more, i would suggest some of the easier LPS corals... like bubbles, favites, hammers, you could also do some softies.. like toadstool (sarcophyton) or the cauliflower.. fairly easy softies.. stear clear of SPS corals..