I have heard of this happening before.  

I just ordered a new reciever for my home theater and I now see a double charge on my account just a few minutes later.  Is there a reason for this?

Charge or pending? If a double charge, call them and ask them whats up.

Wait a couple of hours.  There will be an initial charge (pre-authorization), and then another debit.  The pre-auth should come off within minutes of the 2nd debit.

ETA:  The only time I have seen this NOT to be true is in the case of Hotels or Rental Cars...  This should only apply to debit cards

I had that happen. I called the store that did it and they said they discovered the error and reversed the extra charge. They were very nice about it.

Two weeks later after the charge still showed on my account, I called my card company and disputed the charge.

Two days later I had two credits on my account. I called the credit card comapny and let them know that there should be only one credit so they could remove one of the credits.

Two days later there were two credits removed from my account.

ARRRGGGHHH.

I got fed up with them. I called back and explained the situation once more. They Finally got it right but geez!

It is two pending charges.  I guess that one is authorization and will be removed from the account shortly.  This is on my debit card since my wife and I have no credit cards.

I did not have this happen when I ordered other items for Christmas gifts though.  I suppose that some companies operate differently.

Many "open charge" institutions (hotels, airlines, car rentals, some restaurants) do this on a regular basis.

I have seen hotels charge my debit card on a daily basis, and then make another charge on checkout for the total bill.  It sometimes takes up to 10 business days for the "daily charges" to disappear.

Restaurants generally debit your card for the total bill amount (less tip), then bill for the total amount and refund the original charge at the same time.

Auto rental agencies that actually take debit cards will debit your card for a flat rate (sometimes up to 5X your daily rate, and hold that amount until your actual charge clears (5-10 business days).

It's been several years since I've had an active credit card, but I'm sure the same practices are in effect.

YMMV

Did you double-click on the submit button when ordering?  That can easily cause an online order system to charge your credit card twice.  To be nice, contact the company you ordered from before calling your credit card company.  Chargebacks are very expensive for merchants.  One poor customer of ours sales $5 books, and he often has more money in chargeback fines from Nova than he has total income.  Typically the customers call their cc company and do a chargeback for a bogus reason.  The $65 ridiculous Nova charge eats-up his profit for a tremendous number of books.z