I recently purchased Arkham Horror and wanted to expand my Cthulhu gaming however I never liked having to build my own deck. It was way too much work for me as a more casual gamer. Is there a list of decent decks I can have premade for when friends come over to just pick up and play? Also, I don't know how willing I am to buy multiple expansions, just to get an extra of one card or other. Any help would be greatly appreciated!
What you're asking is pretty much what the core set offers: There is half a deck worth of cards for each of the five factions, so essentially you just combine two factions and you've got an instant deck. You don't have to buy any expansions (asylum packs), though doing so will both improve the game a lot and give it replayability.
With the new model for asylum packs, you get three copies of each card which is the maximum allowed in a deck. With the exception of some of the older expansions, you therefore won't have to buy multiple copies of each asylum pack.