As Embee said, if your ds is having bedtime troubles with no nap, he probalby does still need his nap. Her advice sounds great, in that case!
But my 19 month old doesn't nap anymore. She stopped napping about a month ago. And she doesn't seem to miss it. It was the same story you are describing - I'd try to put her down for a nap, but she'd only fall asleep around 3-4. And then, even if I got her up after an hour, she would NOT go to sleep that night until 9:30-10:30 pm.
I just decided I'd rather skip the nap and have a slightly earlier bedtime.
So...dd2 is usually in bed by 7:45 or so, and gets up around 7:30-8 the following morning. Before dropping her nap, she was about 30 minutes later getting to bed, so she has upped her night-time sleep slightly...
So...it can happen that they give up naps that early. In a way, I quite like it. My 3 year old doesnt' nap anyway (hasn't in well over a year), so I might as well have both of them up...it means we can actually get out and about in the afternoon, you know?
Hope things get better,