My 2.5 yo dd does not nap anymore. We still do quiet time every day. I have tried to do the same things like I do when we put her to bed (the same routine), have put her down for a 'nap' later in the day, tell her to be quiet and if she isn't quiet then she will not get to have a privilege, and also tell her to stay on her bed and read books and play with her stuffed animals. It doesn't seem to work. 5 pm comes when it's time to eat supper and she is a BIG grouch (even before that it starts). She is fussy and whiney and supper is, well, a challenge. It has made me dread this time of day. We have been putting her to bed earlier, e.g. 6:30 but I know this same thing happens every day. HELP! Suggestions anyone?! Thank you!!! :)

Ahhhh, my 3.5 year old DS started this two months ago too...NO naps for the first time...it is KILLING us both! He NEEDS to rest, but refuses! We've tried quiet time with books, music, books on tape--he just throws a fit the whole time he's in there...
We've tried the movie route too, but he needs sleep and he is just as grouchy during and after the show...
He goes to bed earlier and he wakes up by 7am every morning no matter what time you put him to bed earlier or later and still refuses nap....but he SOOOO needs it to not be a nasty little nut and just "so tired he gets nutty/wound up" in the afternoons....
No sugar/sweets, try to get him activity--easier when he's not cooped up due to the cold weather--being able to RUN really helps! Tried the toddler exercise videos...he just looks at me like I've lost my mind! LOL
So...no help, but you're not alone! LOL

My dd#3 started a similiar thing right at about 2 1/2 also. I'd suggest taking some of the advice above and being FIRM. I wish that I had done that in my case. I regret to say that I didn't and have struggled with sleep issues with that child since (she is now 5). What happened is that she'd become so overtired that going down at night became an issue as well by the time she was 3. After months without a nap time I found it nearly impossible to re-start it. I think nipping it in the bud would have been a better route for both her and I. Hindsight is 20/20, ya know?