I do have several ideas on the go: some sit at basic starting points, some a few thousand words in (including the first of 2 prequels to Druid's Daughter), and a couple between 25 000 and 35 000 words along (the latter being a sequel to Spirit of the Stone). I am, however, a great procrastinator, so it usually takes me quite some time to finish a story.
As to where I get my ideas, there's no single source (except my brain) or method I employ. Some stories have started with a scene that popped into my head. Druid's Daughter had its beginnings in a scene with Karen and Jans being confronted by a monster that they had to figure out how to defeat. That scene never made it into the book -- not even remotely -- but the characters were born from that initial idea. My husband helped with suggesting the consequences of Manfred's return, and the end of the story I figured out on a walk through a park. Amrah's subplot did not even exist in the first version. I added it later after a friend suggested that what I had was not long enough for a fantasy novel. That subplot fit in so well with other seeds already in the book that it seemed my subconscious knew what it was about long before my brain caught up.
That happens a lot in my writing, where I go back to add or tweak something and discover that I had already laid the foundation for the insertion at some point.
Spirit of the Stone began as two words: "blue eyes", an image I had while on a train going across Canada on vacation after University. That was it. Stone had further success on a later vacation (this time in Cuba) when I figured out what the Markers would say and what they meant, and yet another big plot point came to me on vacation in Sedona, where I wrote Jolyn's motivation to infiltrate Broman's camp, and why Binor would help. So while it might seem Stone benefited a great deal from my down time, it did take about 10 years to finish. Did I mention that I'm not always a fast writer?
A bunch of ideas come to me as scenes or parts of scenes that I write down and try to figure out if there's a larger story somewhere in there. A couple evolved (are still evolving) from projects I did in school. A few even came as dreams (such as the one sitting at about 25 000, which is my current project). But I'm not one of those authors who can sit down and plot out a whole story. I've tried. I can sometimes get a very general "and then they would do this and somehow end up here" (this seldom works in the end for me as plots tend to diverge from my best intentions), but for the most part, when I start, I begin with little to go on and see where it takes me. Often, the characters write parts of their own story (don't laugh, it's true, and sometimes a little creepy). I have one Sci-fi on the go where the male protagonist really wants to get together with the female lead, but she doesn't think it's a great idea yet (if at all), and it makes it tricky to get on with the story. I haven't done much with it for a couple of years while they sort themselves out.
Anyway, my ideas come when they come, and I do my best to give them a home, even if it takes a while to fully flesh them out.