Well what enzymes you use depends on what you are trying to accomplish.
If you are trying to break down whole gelatinized starch, or convert larger sugars into smaller more fermentable sugars. For the former, I would recommend an alpha-amylase enzyme. Those are typically found in homebrew shops listed as "amylase enzyme", which is misleading. The easiest alpha-amylase to find is usually a bacterial one that works within the 120-165 F range. Depending on the concentration of the enzyme (it can be altered by the supplier or the provider by adding more maltodextrin) dosage can be a few grams to a full ounce. This is typically called the "liquefaction" process of converting starch into dextrins (random sugars). Some commercial products are "Termamyl SC" or "SEBamyl BA".
To further break down the dextrins, or to make a "light" beer, a glucoamylase will be required. This enzyme works below 135 F, on even down to ale fermentation temperatures. This enzyme will break down the larger sugars into glucose, provided enough exposure, can make a 90-95% fermentable mash. Glucoamylase is also known as amyloglucosidase as their scientific names. Some commercial products are "Convertase AG" or "Ultra-Ferm".
Malted barley provides alpha-amylase and beta-amylase to the mash, which means it, converts itself with its own "liquefaction" and "saccharification" steps.
Alpha-amylases can be found in three different temperature ranges: Low, medium, and high. But like I said before, most distributors only have the medium temp one (it is the cheapest).
Hope this helps more than confuses, if you require more information look up "Liquefaction" or "liquefaction enzymes" in Google, there are some good papers on that. Also "The complete joy of homebrewing" 3rd edition has some notes on enzyme uses around pg.218 I think.
Happy Brewing!
Specialty Enzymes
P.S. Sorry if I am not allowed to mention brand names, but there is usually some confusion as to whether the name describes a function or was made up on the fly. All those products are from different providers, so hopefully that makes it better...