It seems that items which provide benefit to AD champs provide more benefit across the board to champs who have a high attack speed. What do champs with slow attacks (like say, Alistar) do to keep up?

An attack speed item benefits a faster attack speed more, because 25% of a big number is better than 25% of a small number.

An attack damage item applies its bonus damage more often on a high attack speed champ.

Crit is the only stat that seems fairly equitable... at least, in isolation. Slow attackers typically have higher base damage, therefore they crit harder than a fast attacking champ. Once you start putting +damage items on a fast attacking champ, however, he starts hitting hard too - but more often.

Yes, you are correct. It is due to the fact that there is no "flat" attack speed increase item. All of them are based on percentage increase.

But, point of the thread is?

Slow attackers generally aren't DPS champions, and will usually only use their slow attacks when they have to (abilities on CD, silenced, taking down a turret, etc.) or to proc lizard buff/sheen/trinity force/lich bane/phage/frozen mallet.

Outside of those things, you're generally better off getting tank/support/caster items instead of DPS ones.

A related question that I've been wondering is - is there a wiki, or google doc, or some other resource where someone has listed all champions' attack speeds (or other stats) in a list or side-by-side format? It's nice to be able to look at the wiki and see that TF has a higher attack speed than Tristana, or see that Poppy has a crazy-high movement speed, but it'd be nice to be able to see where a champ stands in relation to all other champs.

The only slow attack speed champions are tanks and casters and if tanks had fast attack speed thye would just be super OP carries and if casters had fast attack speeds they would just build DPS like everyone else... You aren't supposed to be able to catch up... that's the point.