The answer depends on whether you're on the sell-side or buy-side.
For a seller, closing costs include commissions and possibly transfer taxes, which can take it to as much as 10% overall.
For a buyer, closing costs are usually 1% for an entry-level home around $600K with decent financing terms and a bit more with transfer taxes. If you're paying down points, you can pay up to 4-5% in closing costs. For cash buyers, it's typically around 0.25-0.5% or as low as $20 in some cases.
If the home is a condo, then add about 0.5-1% for condo transfer fees and pre-paid expenses to both sides.