Since we lack diversity between shield choices for each combat style, I've decided to suggest a few things.
Firstly, I have to point out that range lacks off-hand weapons/shields. Among other shields melee has dragon defender and magic has books (requirement lvl 1 O_o), but range has no easily obtainable off-hand object (I'm currently talking about the ones, which have only attack and strength bonuses). I haven't decided on which shield should it be, but here's some possible options: Odium ward, Eagle-eye kiteshield, dragonhide shield. This item shouldn't be hard to get, since getting dragon defender and mage books are easy. As it's other counterparts this item should only give attack and strength bonuses.
There's also an issue with dragonfire shield. It is currently optimised for just melee. My suggestion would be to add a dragonfire shield upgrade kits, which would make the shield suited for either range and mage. To implement it, I would change dfs's current bonuses. After the revision it should be an overall shield: +6 overall attack bonuses, +47 overall defence bonuses and +2 overall strength bonuses. The upgraded shields have the stats of current dfs, but for specific combat style. We can use recoloured dfs models for all 3 new shields: red for melee, green for ranged and blue for magic.
This would give much more shield variation for each combat style, currently melee obviously dominates. This would actually be useful for mages and rangers killing dragons.
I would add these upgrade kits to desert strykewyrms.
Thirdly, rings need more variation. Currently Ring of Stone and Ring of Vigour are so easy to get and they are the best rings in-game. To address this issue I once again recommend adding Imbue scrolls.
These would make the rings untradable and degradable (3000 hits for example) and would make these rings best for each combat style. So once again 3 different scrolls, which would be tradable, but once used to create an imbued ring, they'd become untradable and degradable. To upgrade the ring you would need a Ring of Stone and a Fremennik ring (Berserker ring for melee, Archers' for range and Seers' for mage). We could also add a new overall best ring, which would need Warrior ring and Ring of Stone for it's upgrade: this way Warrior ring would have finally a use as well.
Scrolls would be added to Arzinian avatars in Dagannoth cave.
To prove my point on the rings, I'll point out some facts.
Almost everything else has diversity in this game. There are 4 capes, each of which is best for a certain point (Fire cape for melee, Ava's accumulator for range, God capes for mage, Max cape for overall). There are four amulets (Strength (t), Ranging amulet, Magic (t), Glory (t). Best shields also follow this logic (Arcane, Divine, Elysian, Spectral). Also gloves (Bandos, Armadyl, Battle robe, barrows gloves) and so-on..
It is also very easy to get onyxes in this game. Many monsters drop it: I've counted 8 monsters. You can also get them from Shooting Star, Jad minigame (2 per each game completed) and caskets. Also the requirement for creating onyx rings is just 67 and there are many people who can help with enchanting. Getting a vigour is easy as well, only 5 rounds of pest control (3 at double xp).
Recap for last paragraph: The best ring shouldn't be so easy to get. That's why the suggestion.