There is the "mana on hit" solution, but that only makes the one handed option a clearly superior option with both DPS and sustain. And this also makes ROT and AC OP due to their high proc rate thus devaluing actual designed mana return options like Widowmakers.
There is also the "mana steal" option, but it does not fit the class very well and just makes the item which grants mana steal mandatory. Again it makes designed mana return options like Devouring Swarm pointless since you can just deal more damage and steal more mana with Searing Locusts.
No my WD brothers, the real issue is that some of our designed mana returning options DO NOT SCALE and are obsolete with the increase in mob HP. The below list is a modest buff to those skills with commentary on their usage and skill/gear synergy. The examples are based on the average WD with 150K DPS, 2500 INT and 800 mana.
1. Spined Dart - 0.5% mana steal, reduced to 0.1% by inferno penalty.
This skill returns about 150 mana per second for the average WD and is suitable for all builds as long as they have good DPS. But it takes all your "attack turns" so you are not using you best DPS spell (bears) while you are using this.
2. Widowmakers - the base skill itself should be changed so the spiders always lasts 3 seconds instead of by damage dealed.
This is the mana on hit option. Stacking more IAS allows more spiders thus increasing mana regeneration. Assuming spiders attack once per second and have 2 IAS, the mana return is 96 mana per second. But it takes all your "attack turns" so you are not using you best DPS spell (bears) while you are using this. This option beats Spined Darts when you have 3 IAS or more, which is a lot of IAS, but given that they continue to work for 3 seconds after the last cast means you have more mana overall.
3. Ruthless Terror - 12% mana pool for every enemy hit
Assuming average of 7 targets are hit, gains 672 mana per cast, 42 mana per second. Suitable for those with higher mana pools.
4. Swallow Your Soul - 10% mana pool for every enemy hit
Assuming 5 targets cap, gains 400 mana per cast, 27 mana per second. Suitable for those with higher mana pools. It is purposely weaker than Ruthless Terror because frankly Soul Harvast is a superior skill.
5. Draining Spirit - INT / 100 + 20 mana per second.
Averages 35 mana per second. Suitable for those with higher INT. Very good against elites are it is a cast and forget spell that increases your mana regeneration significantly as long as you keep 3 or more targets cursed.
6. Devouring Swarm - INT / 100 + 40 mana per enemy hit.
Assuming average of 7 targets are hit, gains 385 mana per cast. Very good in getting mana back. The only draw back is the speed at which locusts spread, thus it is suitable at very high MP where even whites take time to kill.
7. Rain Dance - 100% mana per second.
It has limited range and duration of 20 seconds and 123 mana per second is already quite close to unlimited for Skorn users. So just also make it unlimited for our IAS stacking brothers.