Miss chance = 5% + (Target_Defense_Skill-Attacker_Weapon_skill)*0.04%
Another 19% miss are added when dual wielding - those do not apply to special attacks.
Another thing that is required to understand all this: stuff in raids is considered to be Level 63 for all practical purposes. Since NPCs have 5*Level for both their weapon skill and defense skill, the Target_Defense_Skill you see in the formula will be 315 when attacking a boss.

Now here's the fancy part: the actual sources with a few notes

http://www.wowwiki.com/Attack_table?oldid=349774
In example 2, Elliot the dual wielding rogue with 305 weapon skill and +0% hit is attacking a boss. In the shown attack table, Elliot's chance to miss is 24.4% for his white hits and 5.4% when it comes to Backstabs. If we plug the stat setup into the aforementioned formulas, we get
5%+(315-305)*0.04%+19%=24.4% for Elliot's white hits and
5%+(315-305)*0.04%=5.4% for Elliot's special attacks.

http://elitistjerks.com/f15/t7308-dual_wielding_lifestealting_vs_crusader/
In post 5, Mem says the following:
"Therefore the MH does hit more often, especially since styles do only miss for 5 % against Level 60 targets."
By "styles" he means special attacks. The mentioned formula for the miss chance for single wielding works again in this situation:
5%+(300-300)*0.04%=5%. Works out.

http://leftoversraiding.org/index.php/topic/839/1/glancing-blows-and-you.html
While this post is mainly about glancing blows, the author mentions the values of an attack table a single wielding player with 300 weapon skill and 0% +hit would have when attacking a boss from the front.
"If you're tanking a level 63 boss, the following events can occur: 40% glancing blows, 5.6% dodge, 5.6% parry, 5.6% block, and 5.6% miss"
Applying the single wield miss formula:
5%+(315-300)*0.04%=5.6%. Works out.

http://www.wowwiki.com/Weapon_skill?oldid=349298
"With no +skill/+hit gear on, attacks made by a dual wielder against a level 63 mob will have the following table from the front"..."24.6% Miss"
Applying the dual wield miss formula:
5%+(315-300)*0.04%+19%=24.6%. Works out.

http://elitistjerks.com/f15/t6291-not_another_rogue_thread_glancing_blows/p5/
"Data is from Ebonroc/Flamegor/3x DeathTalon Wyrmguards (or whatever the lvl 63 ones are)/Chromaggus tonight, so, all level 63s. 304 sword skill (gnome, Maladath.)

1311 swings
544 glancing (41.5% glancing)
339 crits (25.8% crit)
153 non-crit white hits
189 misses (14.4% miss)
80 dodge (6.1%)
6 parry (negligible)

+hit gear varied according to need (FR, mostly), average of 10% +hit."
304 weapon skill, about 10% hit, attacking a boss. Appyling the dual wield formula on this example, we get:
5%+(315-304)*0.04%-19%+10%=14.44%. The player observed 14.416% misses - considering we only have a sample size of 1311 swings, a slight aberration is to be expected.

http://elitistjerks.com/f15/t6291-not_another_rogue_thread_glancing_blows/p9/
Some folks are theorycrafting some maximum crit on white hit build here. deric writes down an attack table assuming +12% hit (and most likely no +skill).
"Crit: 41.8%
Hit: 0%
Glancing: 40%
Miss: 12.6%
Dodge: 5.6%"
Time for the dual wield miss formula to shine:
5%+(315-300)*0.04%+19%-12%=12.6%. Works out.

web.archive.org/web/20060516141644/http://forums.worldofwarcraft.com/thread.aspx?FN=wow-warrior&T=942763
"With no +skill/+hit gear on, a dual wielder vs a level 63 mob will have the following damage table from the front: 5.6% dodge, 5.6% parry, 24.6% miss, 5.6% block, 40% glancing blow, 18.6% combined hit + crit. Attacking from the front prevents dodge and block giving 29.8% combined hit + crit."
"For 2hers it is not as bad.
You have 5.6% miss, 5.6% dodge, 5.6% parry, 5.6% block, 40% glancing, 37.6 hit/crit. This is a 37.6 + your +hit crit cap from the front, 48.8% from the back "
Two quotes from the same thread, one for dual wielding and one for single wielding (using a two handed weapon does not influence your chance to miss).
Using the formulas yet again:
5%+(315-300)*0.04%+19%=24.6% for the dual wield scenario,
5%+(315-300)*0.04%=5.6% foe the single wield scenario.

http://elitistjerks.com/f15/t7220-skill_ranged_you/
Pretty straightforward right here:
"For melee, chance to miss against a boss would thus be 5.6% (5 Defense gained per level)."
I don't even feel like making use of the formulas anymore.