For lightweight in Python, I started on Bottle, but found Flask to be more to my liking for very small projects/web services.
Mostly Django here; if you know the framework well, most things are very quick, but I wouldn't particularly call it "streamlined." Plus that up-front time to get to know it might disqualify it, and lightweight it definitely is not.
My Ruby friends tend toward Sinatra for small projects.
Do you have any good examples? I'd like to try Flask, but the only examples on the flask site are very, very small sites, and don't help at all with learning to structure something larger.
Mostly Django here; if you know the framework well, most things are very quick, but I wouldn't particularly call it "streamlined." Plus that up-front time to get to know it might disqualify it, and lightweight it definitely is not.
My Ruby friends tend toward Sinatra for small projects.