Free SF Reader links James H Schmitz's short story collection "Eternal Frontier", compiled by Eric Flint. While the collection has a lot of stories, 6 of them are online: "Adventures in Time and Space", "The Big Terrarium", "Summer Guests", "Captives of the Thieve-Star", "Caretaker", & "One Step Ahead".
Note: My personal experience with Schmitz is limited to his best known work - very readable space opera novel titled "The Witches of Karres". I haven't read any of these 6 stories.
QuasarDragon links Charles Coleman Finlay's "The Political Officer". I'd read it long back as part of Dozois' annual Best of Year #20 anthology (2003). I don't recall a lot of plot details, but I'd rated it B; it must have impressed me as ok though not great.
Eoghann Irving's post titled "The History of Science Fiction - The 19th Century" at Solar Flare lists some of the classic sf works of nineteenth century, along with short descriptions. I've read only 3 of the lot & they are important works - though not always very gripping & not always science fictional. He doesn't link online copies, but they should be easy to find with google - all should be public domain. For me, the most interesting thing was the list of titles worth looking up - at least a couple of names I didn't know.
Credits: I found Irving's post via SF Signal.