+1 swords are boring. I talked about that here.
Can we apply the principle of "active, fantastic magic" to other common magic items?
Flaming sword
I think the flaming sword is particularly pathetic. It sounds so cool. A flaming sword! What does it do? Ah, "additional damage." Wow.
Let's hit this one like a hammer.
After the first sin, Man and Woman were cast out of the Garden of Eden, and an angel set to guard the gates with a flaming sword. In time, the garden withered and the angel grew negligent. This is his sword.
When drawn from its scabbard, the flaming sword erupts into fire.
It sheds light and heat like a bright torch. Although you are never without light as long as you have this sword, it is uncomfortable to hold. Too bright. Too hot. You sweat while it's drawn.
The sword is as hot as a forge. You can start fires with the sword easily.
Roll an additional +d6 when you attack with this sword (for a total of 2d6 damage). Make this extra dice red, for style and pizzazz purposes.
If you ever deal 6+ damage with the flaming sword, your target catches on fire. They take an additional 1d6 damage every turn until they spend a turn putting themselves out. The GM arbitrates how fires are put out. Throwing themselves in water would work (but would ruin carried scrolls, etc.). Rolling on the ground might work, but would break potion bottles.
Moreover, given time, you can cut through any material that will melt at forge temperatures. You can push the sword through a lock, easily hack open wooden doors, and melt down lesser swords.
The blood of an innocent will cool this sword's fire forever. If ever used to harm someone truly innocent (a child, someone who just undertook confession, etc.), the sword's magic is lost.
Ring of protection
Ring of protection - another set it and forget it item. But how can we make it active?
The ring of protection is writ with runes of invulnerability. While worn, the hand on which it sits is as invulnerable as mithril.
If you are not carrying anything in that hand, you may use your hand like a light shield by catching and deflecting blows with your bare hand.
Having a free, invulnerable hand is very handy for gambits. When it would be helpful (GM's discretion), you only roll one dice instead of two, succeeding on a gambit on a single hit. You simply twist weapons away from the hands of combatants by grabbing the blade.
Additionally, you can use your hand as an invulnerable tool--up unto the wrist. You can dip your finger in acid, hold open a door that slams shut, or catch a swinging pendulum blade. Still, the ring does not confer super strength or other protection. The force of a blow might shatter your shoulder.
You can elect to shatter the ring of protection to automatically pass a saving throw. You must make this decision before making the roll.
Boots of speed
These winged boots weren't meant for you, mortal. You are moving at god-speeds. You are killing yourself.
When you click your heels together, you rocket forward. Your body is faster than your mind. You're moving faster than you can see. This is disorienting.
While traveling overland, you blast forward. You can move 1 hex (6 miles) in 10 minutes. This causes 10 damage to your body as your joints and muscles and bones are put under incredible strain.
While traveling in close quarters (like in a dungeon), you instantly move a distance equal to your normal walking pace. This functions essentially like a teleport, and is disorienting. Take 1d4 damage as you clip the edge of a companion's shield or stop yourself by slamming into a wall.
During combat, you move your normal walking pace in addition to any other actions you take during this round. You take 1 damage from accident and strain when you do this, but you also deal +1d4 extra damage from inertia while making attacks. If it matters for your system, you automatically disengage from enemies when using the boots in this way.
Bag of holding
So I'm against the bag of holding on principle. Magic items shouldn't negate the essential dangers of the dungeon*. If you trivialize what you can bring on a journey, you trivialize the resource management of a dungeon crawl. But, uh, here's an alternative.
It's a pig. It looks dumb as hell. But if you scratch it behind its ears, it opens up like a pack.
The pig of holding can hold 20 slots worth of items. It follows beyond you, sometimes bumping into you and stepping on your heels. If unattended, it sometimes wanders away to press its head into a corner, so it's a good idea to tie a loose leash to it. It eats garbage, but you do need to feed it or it will die. It's just a pig after all.
Dimensional magics get all twisted up inside the pig. Casting teleport or dimension door on the pig, placing another dimensional artifact (portable hole, etc.) inside the pig, or similar results in a magical catastrophe. Draw on your favorite Bad Magic Shit table.
Eh. I don't love this one. It's maybe a little weirder but it's not necessarily more magical.
* Did you notice how the flaming sword (above) did this? Yeah. Bad game design. The guy who wrote that sucks.
Belt of giant strength
I like a belt of giant's strength as much as the next guy, but always thought it was interesting when it set your Strength directly to a number instead of giving you a bonus. Is there a way we can make this more active?
While wearing this belt, you have the strength of a giant.
Let me clarify. You have the strength of one, specific giant. Perhaps you have the belt that channels the strength of Grom the Unwieldy. Perhaps you have the belt that channels Oglethorp of the Deep Nostrils. They were created by dwarves long ago after the Second Giant Wars as a condition of their surrender. When you use the belt's powers, you make the bonded giant weak and tired. If that giant ever dies, the belt ceases to function. Obviously, giants hate this and will attack anyone wearing these belts on sight.
Once per day, you may invoke the power of the belt to perform some Herculean task. You can lift a portcullis, pull down a column, divert a river through sheer strength, wrestle a lion to the ground, etc. This task is automatically successful if it is at all possible through actual main-forte. This power refreshes at the dawn of every day, per the ancient bargain.
Additional resources