Before we can talk about spending bitcoins, you have to have bitcoins first right? I’ll try to simplify this process as much as possible considering the fact that worst part about Bitcoin tends to be those instances that involve fiat currency.
The site I currently use is BitWage (http://www.bitwage.co). This website is great for people who get their paychecks direct deposited into their US bank account. The way BitWage works is they give you a direct deposit number, you provide them with your Bitcoin address and when your paycheck goes through they deposit the equivalent bitcoins into your Bitcoin address.
BitWage says that they do not charge a fee but I have found that the exchange rate is usually about 1% higher than those on other exchanges, so you are essentially paying 1% for the service. It is good that you don’t have to worry about becoming a day trader on the exchanges and it’s all automated and your bitcoins are never under someone else’s control.
Many companies allow you to split your direct deposit between two or more bank accounts so you can have maybe 80% into your bank and 20% in bitcoins. I personally convert 100% of my paycheck into bitcoins.
Another option is to go through an exchange. In the US I have used CoinBase (http://www.coinbase.com) which has been around for a few years and is one of the most secure exchanges today. Coinbase is fairly easy to use, you give them your bank account information, then either immediately get access by using your online bank login credentials or they verify in 24 hours by depositing a tiny amount of money and have you verify the amount. The initial amounts you can exchange are usually around $500 or so and go up with use.
Most recently when I sold my house I used itBit (http://www.itbit.com) to do what is called an Over the Counter (OTC) trade which allows for large purchases of bitcoin without moving the price up or down in the process. The cost was $10 on their end for the wire transfer (my bank charged me $30) plus .1% for the transaction fee. They contact both seller and buyer via Skype and coordinate the purchase price in large blocks of bitcoins (like 100-200 at a time). They are completely regulated in the US and did their due diligence with my purchase.
When using an exchange, it is highly advised that you keep the money on the exchange for as short a time as possible and once you get your bitcoins exchanged, take them off of the exchange into your secure wallet. Remember that you do not own your bitcoins unless you have the private key.