What is a good sub to buy?

I had a older alphasonik 2 years ago in my truck 10in powered with a 400watt alpine amp. It sounded great it wasnt major or anything but I just wanted it to give me some more bass. I've been looking at the new ones and not sure if they are still made as good as the old ones were. I dont want to spend a lot, not looking for a major system that you can hear for blocks. I have a 250 watt amp right now which will do for right now until I get money for a new one. Oh and also looking for new door speakers that have some good bass(I dont do sub when I have my radio on just ipod)Any recommendations?