Valleywag has a long list of tips including:
Pitch editors by sending them one-paragraph emails describing short, say 300-word articles you'd like to write. Aim for the lowest person on the masthead whose title includes the word "editor," except for "contributing editor" which means "freelancer in jammies."
AVOID: Hardware product reviews. Do you want a house full of boxes and a divorce? Even Walt Mossberg's wife flips out about the boxes. Plus eventually, someone will steal a review loaner camera or laptop on its way back to the manufacturer, who'll then invoice you for it. Great: A $2,500 bill for a $500 article.
Do software reviews. Most companies will give you a reviewer's guide you can just rewrite. Find one bad, reproducible bug. Google's good for that. File.