Oh yeah, you asked for samples. Seems I keep posting the same ones over and over when this topic comes up (which it does every few of weeks or so), so I'll try a few different ones to illustrate particular situations. And maybe I'll bookmark this post so I can point re-use it next time :-) All images shot with my K200D.
Here's one where light was good enough for f/4, ISO 400, and 1/60" - relatively bright office lighting, and some filtered daylight coming through the window blinds. f/4 of course gives more DOF than f/2.8, and I took advantage of the opportunity to go there because while I was obviously interested the subject (hi, Mom!), I wanted to the office itself to be a significant element of the picture. This is a scene I'd probably have been better off shooting with my 28 to better capture the surroundings. I had to step back a bit further than I'd have preferred to take this, and I still chopped of the desk rather abruptly. But a 50 would not have allowed me to get the shot at all.
Here's one with direct window light only, but quite a bit of it (a sliding glass door, actually). So I was able to use used ISO 400 and 1/60" again, but I chose f/2.8 this time, since I *wanted* to blur the background. If I had my A50/1.7, I might have used it at f/2 to blur the background more, but I'd have been fighting DOF big time. It would have been better to find a way to compose the shot without the background distraction.
Normally, when you don't have much sunlight coming in through a window, f/2.8 isn't a choice - it's a necessity. Here's one lit primarily by ordinary household lamps, but reasonably brightly. f/2.8 again, ISO 800, 1/30". DOF comes close to covering both the stuffed penguin and my niece, but as you may be able to see, it isn't *quite* enough. I think it works here, but this gives you an idea of why I say that apertures larger than f/2.8 are sometimes less useful than one might think: you often have to sacrifice the focus on part of your subject even at f/2.8:
Overall, my usual assumption is that I'll shoot f/2.8, ISO 1600, and use 1/30". I probably take more pictures indoors at those settings than any other. I usually just make those settings in "M" mode, take a test shot, and assuming it's in the ballpark, I don't think about exposure again. I find that 2.8 / 1600 / 1/30 covers an awful lot of indoor situations. Sometimes the exposure is perfect, sometimes a little overexposed, sometimes a little underexposed, but nothing not easily deal with in RAW PP. This one, for instance, required a 1/2 EV push:
Here's the worst-case scenario: a subject hiding in a dark corner of a dark room. Luckily, it's a pretty light-colored subject, but even so, I needed to go down to 1/10" at f/2.8 & ISO 1600, and then still needed to shoot underexposed and push it one stop in PP (meaning this was the equivalent of ISO 3200). Luckily, the subject was content to sit still long enough for 1/10" to yield a reasonably sharp picture: