If you complete all fifteen of the Daedric quests, the final prize is a major stat boost. You can select any of the three major skill sets: Combat, Guile, or Magic. Each gives you a 10 point permanent boost to the related stats and some of the related skills. It is definitely worth it considering all the other good items you will get while doing the Daedric quests. You can activate up to 14 at once if you are at a high enough level. The final quest requires level 21+, and you must have completed all of the other Daedric quests.
Get a Sigil Stone of your choice and either an enchanted item or regular item. Enchant the item with a Sigil Stone, then use the "Duplicate items" glitch on it to get a permanent stat boost to whatever the item was meant to increase. Repeat this with the same or different enchantment to continuously get stat boosts in that category. You can then sell the extra copies for some gold. Note: Do not try to duplicate more than 250 copies of an item or the game will freeze.