Well, for me at least, I have a couple of favorite fish. I really like my twig catfish. They clean nicely, they look likee goofy sticks, and how many fish will docily let you pick them up and pet them if you want. Literally. http://www.fishforums.net/index.php?/topic/143031-twig-catfish/ . I used to have a leaf fish too, unfortunatly it was a bit too carniverous for my tank, and it ate a few too many tetras. It was awsome though, it would hide in the plants, pretending to be a leaf, swimming up to things sideways with the currents. The Roseline sharks are the showpieces of the tank, but they don't have much personality. I like the clown loaches too. They are about the closest you will get to a puppy in aquariums. The Siamese algae eaters don't look like all that much, but they do a damned good job of cleaning. I guess overall either the roselines or the twig catfish. The smaller ones are nice to look at, and the angle fish, but they don't have much personality either. And the plecostimus annoys me. So does the kissing gourmi. I grew a bunch of baby salmon for a Jr. high school science program, they were really cool to watch grow, but they took alot of specialized equipment, and we had to let them go before they got too big.
Plants, I'd say my favorite one overall is the bananna plant. It looks goofy. If you can find them, baby mangrove trees make an ideal addition to your sump for filtration in a freshwater or saltwater aquarium. underwater bamboo looks neat too. One of my other favorites is madigascar lace leaf. http://en.wikipedia.org/wiki/Aponogeton_madagascariensis It looks like someone made a plant out of a flyswatter. If you need a mix of other plants, I have a bunch of ones I use.
For invertebrates, My favorite of all time was "The Snail". It was a male yellow apple snail that grew to the size of a tennis ball when I was down in houston. I tried a few apple snails after him, but it just wasn't the same, and i was getting an infestation of pest snails, so I got the clown loaches instead and they are not compatable with new snails. I've also had freshwater clams and muscles. you have to be careful with them, as their offspring can attack fish in the free floating stage. A simple UV water sterelizer takes care of that though. Having live clams at the bottom of the aquarium is definitly a conversation piece. I think my other favorites are the shrimp. I've actually managed to breed cherry shrimp down in my sump. The larger bamboo shrimp tend to be more interesting to watch and safer around larger fish that will otherwise eat them. Stay far away from crawish and crabs unless you enjoy watching them eat your fish or escaping the tank and dying.
I have had frogs in the tank occasionally, i've never really had good luck with them. Had an eel once too. that was kind of neat.
