I'm interested in mining and would like to know if there are any consumer grade computers available that can mine any of the alternative coins. If so, what computers and which coins do you think would work fairly well?
As mentioned almost any is able to mine coins - the question just arises about profitability.
There are some mining pools, that offer to switch the coin mined automatically depending on which coin is the most profitable at any point in time.
Examples of those pools are:
Simply put all consumer grade computers "could" mine bitcoin and other altcoins, the question you're probably interested in is regarding profitabiltiy.
At this point in time people are still mining scrypt based altcoins with specially built machines with multiple high performance GPU's. Whether this is profitable depends on your circumstances for example power price per kW/h, the price of the coins you're mining and the cost of the rig you build/buy.