Where can you get the best weapons in elder scrolls IV oblivion

Umbra! if you go to the Alyeid Ruin Vindasel, it is south-westish of the Imperial City, you can make your way through it and find "Umbra". If you manage to kill her, you get her extremely powerful jet-black one handed longsword that has soul steal for 30 seconds on it. If you have Shivering Isles, there is a quest where you go into a grotto. When you enter it, you will fight an exact duplicate of yourself. When you defeat it, it will drop Shadowrend. Shadowrend is a very powerful two handed weapon. (Depending on your preference, it will be either an axe or a sword). It is also jet-black.