I love Arrested Development and I'm still hoping the film will be made. It wasn't cancelled because it wasn't being watched, it had really good viewing figures, the problem was with the people who were watching it. Apparently, the demographic who watched it didn't spend their money on the products that were advertised in the breaks. Not sure how true that is, but it's something I've heard. I miss that show so much! Shame they had to fit 18 episodes into 13 to finish it.
Farscape was awesome, but it could be argued that it ended as it did have the mini series to wind things up. The first ending was a proper cliff hanger though.
Better off Ted is another one that I miss. Only started to watch that recently and I was devastated when I found out that the "first" season was the only season. I didn't realise that it was 2 thirteen episode seasons! It's the only series I've kept on my PVR so i can go back and watch it until I get a blueray recorder anyway...