High value of informal code inspections, even for single developers
Although I have participated in more heavy-weight code walkthroughs on projects developing "mission critical" software, I believe that usually the much more light weight code inspection process gives more value per cost.
Here is simple form that I use. If a few people are going to perform a code inspection on a code module, each person receives a line-numbered listing (I use a little Python script to generate these) with an inspection form stapled to the front. Everyone spends sufficient time to go through the listing, noting any potential defects on the form. The group then has a very short meeting to quickly go over the findings. The person who wrote the code module takes all of the forms away for her own use in correcting any defects.
I know that this process sounds light weight, but very little time is spent, and usually to very good effect.
I am working by myself on a project right now, but today I am still performing a code inspection on everything that I have written in the last 6 weeks. I am skipping filling out the form :-) No substitute for very carefully reading over every line of code as a prelude to integration testing - saves time.