As you mentioned linear regulators, I'm assuming we're talking 'buck' here?
Considering the hassle working with switching regulators (extra parts, conducted noise, radiated noise) I don't have a 'default and easy' regulator I use. Although as far as 'common' goes, the MC34063 springs to mind. Not the best efficiency in the world, but every circuit I've built with it has worked like a charm. It's found in countless 'in car' chargers, console adapters, PC motherboards/cards, etc.. which require medium current regulation. Its everywhere.
National semi's 'simple switchers' would be up next for medium current bucks.
Everything else *I* have used has either been high efficiency boost (portable apps that need 12-36V from batteries) or synchronous boost (MCP1640) for single cell to 3.3/5v apps. Just found what chip did the job as oppose to lean towards one brand/chip. - I know thats not 'what popular', just saying that, I'm not sure many engineers would stick with 'one solution' given the vast number of different chips available, as well as the long list of parameters one uses to pick them.
damnit Jony....I only got one, he listed them all! uc3842 - found everywhere....