For some boss fights where the vast majority of the time you're simply beating on a single big baddie, what are the most effective spells (and runes) for the Wizard to use? Such a build might not be the "best" as you're prone to dying, but it would be good to know where the top is as a baseline and perhaps build beefier from there.
Your new question is fairly dependent on a lot of factors, but you want to start you build by looking at a combination of Ray of Frost (either Snow Blast or Cold Blood). Snow Blast is technically our highest DPS, but it takes time for it to ramp up. If you are doing hit and run, then Cold Blood will serve you better and leave you more mana to work with.
Magic Missile with Charged Blast is going to be your best single target Primary unless you are trying to trigger a proc of some sort. If you are, then Electrocute is were you want to look for that. A good primary is important to keeping the damage up while you regen mana.
For raw damage increase, Force Weapon is an obvious buff worth taking. Sparkflint will increase both your attacks and provide shots of its own.
Hydra is probably the best spell for adding additional single target damage for little mana. The other Force and Conjuration spells are geared more towards AoE. Conflagration will cause the Hydra to give you an additional 10% boost to your damage.
Slow time can be used to boost damage in several ways in addition to providing some defense. Stretch time will provide a nice 10% increase to attack speed.
Arcane Dynamo, Conflagration, and Glass Cannon are going to be the passives you want to look at first.
So to sum it up, assuming single target with no worries about survival here is a good start:
Ray of Frost (Snow Blast or Cold Blood), Magic Missile (Charged Blast), Magic Weapon (Force Weapon), Familiar (Sparkflint), Slow Time (Stretch Time), Hydra, Arcane Dynamo, Conflagration, Glass Cannon
Ray of Frost is a great single target spell that starts around 200% weapon damage. You can rune it so that it does more damage the longer it is on the target or to not cost any AP at all. When the slow does effect a boss, it gives you more time before you have to move and has a quick casting animation. Also combos well with some of the other abilities.
Ray of Frost is the best choice for the boss fights that have few adds involved, but to be honest, most bosses in D3 don't really allow you to just nuke them endlessly. You're better off trading some DPS for defensive/CC abilities. (In hell & inferno difficulties you won't have a choice in this.)
My single-target DPS uses Magic Missile (Charged Blast), Ray of Frost (Snow Blast or Cold Blood), Mirror Image (Mocking Demise), Frostnova (Bonechill or Cold Snap depending on whether you prefer higher DPS or more CC), Teleport (Fragmented), and Energy Armor (Pinpoint Barrier).
For passive skills, I took Prodigy, Conflagration to augment your Sparkflint's damage**, and Glass Cannon (beware Glass Cannon - nearly all bosses can potentially 1-shot you with this active).
The constant mirror images give the boss something else to fight while you nuke (yes, i said constant: your Teleport is giving you mirrors too now XD), and Frost Nova can aid in keeping the boss at a distance. The Mocking Demise mirrors do not provide particularly impressive DPS, but it's a free nuke from a defensive skill.
If you take Illusionist in this build, you will be doing a ridiculous amount of kiting but will still be free to pound the boss for long periods. So trading Conflagration or Glass Cannon for Illusionist may be preferable over the long run as you cannot deal out DPS when you are dead.
The most important thing to remember about rays is that you need to stand still to cast them, making you that much more vulnerable. Sometimes it is better to not think about a fight purely in terms of DPS unless you already have the means to keep the bad guy away from your face.