Well, paella is not really tapas but a main dish.
Although others have already threw in some paella recipes (I'm still shocked at some of the ingredients, but hey, I still love some of my own Italian recipes and don't pretend them to be 'authentic') here you have a couple typical tapas dishes.
For a simple, effective and authentic tapas dish, get some (fresh) anchovies, keep them overnight on vinegar with some garlic and oregano. Make a flour-salt mix, dip the fishies in the mix, then on beaten egg and fry on very hot oil (olive, preferably). Gut the anchovies only if they're big, otherwise cook (and eat) them whole.
Instead of vinegar, you can marinate them on 2 parts of vinegar and 1 part of white wine plus the garlic and oregano.
This one requires some more work, but you can just make big quantity and stock for months. Again, fresh anchovies, cut head, remove gut and backbone so you get two clean fillets still held together just by the skin. Then make a mix of vinegar, water and salt, put a single anchovy in the mix so that it floats in the middle. If it sinks, you've put too much vinegar, if it floats, then too much salt.
Keep them for a couple of days maximum, then take the anchovies out, add oil, parsley and some garlic and ready to serve. You can keep the rest in oil for months.
Another very simple one: put half a finger-deep oil in an oven-proof dish with some slices of garlic. Heat for about 10 minutes on a very hot oven, then put as many (preferably fresh, already clean) prawns for about 5 minutes and it's ready. Once the prawns are gone, dip bread until the oil is gone, too.
All of them are very, very simple to cook, so taste will mostly depend on the freshness of the materials.