I posted a reply to a query about types of Irish whiskey in another thread on the "Everything Else" forum a while ago.
viewtopic.php?f=38&t=1162#p10709
A couple of people were kind enough to say they liked it. I have modified it slightly in case anyone else finds it useful. It might be even better to start listing the different brands under the headings I've identified, and give links to the tasting notes (where available) that members have supplied elsewhere on the forum. But I don't have time to do all that now! If someone else is interested enough to make a start, that would be great.
There are essentially four types of Irish whiskey that you can buy:
Malt whiskey
Single Pot Still/Pure Pot Still
Single grain
Blends
and as there are three components to blend, there are four types of blend:
Malt and Pot Still - some people don't like to refer to this category as a blend, because they feel a blend in normal parlance includes grain whiskey, and this category does not. We could describe this as a "pot still blend" to make clear that all the whiskey is made in a pot still. [Hat tip to David H and Fionnán.]
Malt and Grain
Pot Still and Grain, and
Malt, Pot Still and Grain
Most malt whiskey that you can buy is single malt. Single malt Irish whiskey is from a single distillery, in a pot still, made solely from malted barley. [In Japan some malt whisky is made in column stills; there is a whiskey made from malted barley in a column still in Scotland which the Scotch Whisky Association does not allow to be called "single malt".] Malt whiskey is made in Midleton, Bushmills, Kilbeggan and Cooley, but Midleton doesn't market any single malt, it's mixed with its other whiskies. [There was a single malt available in the US in the 90s called Erin Go Bragh which was reportedly from Midleton, but it wasn't very good.]
Kilbeggan Distillery Reserve is a malt whiskey but not a single malt - it has been distilled twice, first in Cooley, second in Kilbeggan. Although a similar process is followed in some distilleries in Scotland I am not aware of it being bottled separately, so it may be unique in that regard. [Hat tip to Michael Foggerty for this.]
I'm not aware of any "vatted Irish malts" - that is, a mix of single malts from different distilleries (as opposed to a single distillate which is distilled in two distilleries).
Single pot still or pure pot still is made in a single distillery, in a pot still, from a mix of grains. This is the "classic" Irish whiskey style. It was developed because there was a higher tax on malted barley so unmalted grains were added. In recent years it has been a mix of malted and unmalted barley. In past years other grains were used. Midleton was the only distillery making this whiskey style from the mid seventies to this year. Kilbeggan distillery is now making single pot still and is using oats as well as barley.
Grain whiskey is made from a mix of grains in column or continuous stills. This is made in Midleton, Cooley and I think Kilbeggan, but Midleton and Kilbeggan don't bottle their grain separately. Cooley bottles a single grain under the Greenore label.
As noted above, blended Irish could be a blend of malt and grain whiskey; malt, grain and single pot still; grain and single pot still; or, malt and single pot still. In theory it could involve a blend of grains from different distilleries but that is probably unlikely to happen (or to be marketable).
All the whiskeys (malt, grain, single pot still) in Midleton's blends have been made in Midleton. All the whiskeys (malt and grain) in Cooley's/Kilbeggan's blends have been made in Cooley or Kilbeggan, mostly Cooley as Kilbeggan has only been recently reopened as a distillery. The malt in the Bushmills blends (Original, Black Bush, 1608) comes from Bushmills, the grain is from Midleton (to date at least, though that may change as they're not owned by the same company any more).
Bushmills, Cooley and Kilbeggan do "wood finishes" - that is, they mature the whiskey mostly in ex-bourbon casks and then finish some in other casks, usually sherry, sometimes madeira, port, rum or non-fortified wines. They also market whiskey which is not finished in wine casks. Some Bushmills malts are "triple wood" - matured in Bourbon, then sherry, and finished in port casks (the 16 year old) or madeira casks (the 21 year old). Midleton don't do finishes, they mature some stock in Bourbon casks, some in sherry casks, and then marry them in certain blends.
I may have made mistakes in the above - feel free to correct if you have better information.