There are way too many plants that fit into this category to even try listing them. Normally it's best to try sticking only with plants that you know will grow. Sometimes only part of the plant is toxic such as the leaves or the flowers or even just the roots. Some release the toxin into the water and others just hold it till eaten. Other times seeds are released and they may be the only part that's toxic. Due to the possibility of losing all your fish due to poison I do not suggest experimenting unless you know someone who is heavily involved in the plant industry and it's biology or the fish community who can tell you more about the plants and what happens to them if submerged in water. You should check out "What types of plants can I grow in my freshwater fishtank?" for the FAQ covering where to find info of plants that are best in the fish tank.