As we all know, classes that can cast spells will always be stronger than those that cannot. There's no quick fix for this disparity - every single spell printed is another option for the casters, yet sword-swingers have to pick from a variety of band-aid-type patches to make them more viable. So what if, instead, they had a way to cast spells of their own?
All right, yes, there is some rather lengthy fine print to that statement, but there is an efficient way for anyone to sling a spell every now and then. All it takes to qualify is the ability to swing a stick around - the harder, the better. Enter the spell-storing weapon special ability from the Dungeon Master's Guide: essentially it allows a spellcaster to store any one targeted spell of up to 3rd level in a melee weapon. Whenever the spell-storing weapon hits a creature, it can immediately cast the stored spell on the foe, regardless of who or what its wielder is. It can only store one spell at a time, but it can be refilled any number of times. Now, chances are you aren't going to take the time to store a spell in a weapon mid-combat, so it amounts to one quickened spell on the first strike in a fight. If the spell was stored the day before, it even amounts to one extra spell slot. Not bad for a +1 bonus!
So which spells are the best choices for your rider effect? The restriction to targeted spells means no Rays are permitted, so things like ray of exhaustion and enervation are off the table. The level cap of 3rd means you won't be wishing upon any stars - or anything else, for that matter. Still, there are a healthy number of effects that most assailants won't want cast on them within that criteria, some particular standouts being listed here.