We've looked into it quite seriously. It's the only way I'd consider raising a child. I've specifically researched international adoptions quite thoroughly, talking to adoption agencies that specialize in a couple different countries of interest. Every country is drastically different in their policies.
Most countries are now adopting the policy where children must be available for in-country adoption for the first 3-5 years of their life, and then are available for foreign adoptions. Infants are hard to come by, if that's something you're interested in.
The costs vary. Generally the country's fees are between $15-20k, and the travel expenses and domestic fees you pay on top of it are another $10-$20k. Some countries make you travel their twice (for up to several weeks at a time); a few only require one visit (though generally longer). Some countries match you ahead of time, others tell you there are options but you have to meet the child first before accepting the referral.
There is/was an adoption tax credit up to $13k, but it's expiring this year and is only renewing for special needs adoptions as far as I can tell. Some companies offer adoption credits in their benefits (my husband's offers $3k). It's basically a $30k+ investment though, no matter how you look at it. Kind of frustrating since "making your own" is basically free with insurance.
The timeline is different in different countries too. The quickest I've ever heard of is a year for a special needs child from China. The average wait for a healthy chinese baby though is around 6 years (and you can't even apply until you are both 30). Most countries for a healthy child under 5, the wait is ~3 years.
If we decide to have a child, it will be from a foreign adoption. I just can't justify having my own when there are so many children who need their own homes (and whose "disabilities" are often easily fixable in the US). It really depends on how important it is to my husband though. I would be happy never having a child, but I think one day he's going to want one.