A trick I sometimes use is to leave something broken (or unfinished) when I quit working. It's easier to get back up to speed by picking up where I left off than by starting something new from zero.

for me: start programing in the morning and don't check my email or any "leisure" websites (like hacker news) until after lunch. I've found that I only have about 5 hours of hard-core coding in me in a day, so I try to use that up in one block in the morning and work on non-coding B.S. afterwards...

I agree with pg: coding is like writing. I use the same strategies trying to stay productive as a coder that I did fighting writer's block while working as a technical writer...

managing a running server, on the other hand, is not like writing...

it's a %$#%ing nightmare ;-)

The "Morning Pages" concept from "The Artist's Way at Work" http://www.amazon.com/dp/0688166350

Write three pages in longhand first thing in the morning every day. Can be stream of consciousness, a journal, a story, or even "I don't know what to write" over and over.

There are a number of good techniques in the book, but this is the best one to start with.