Vector NTI if you want a very versatile, flexible program and intend to keep up the dynamic license that Invitrogen now charges for. Serial cloner if you just want to make some simple vector maps or do direct subcloning.
The best software, hands down, in my opinion is SnapGene (www.snapgene.com). There is a free version with some functions, but it's worth it to buy the whole software suite. I have been an alpha tester for several years now on this software, and it is far superior to Vector NTI and DNAstar, in my experience. It will change your cloning life and it is straightforward and intuitive to use. Best of luck with your cloning!
Try VectorFriends at http://www.vectorfriends.com. It combines various types of cloning simulation, sequence analysis, and data management into one application.
We are using Vector NTI for plasmid drawing and are quite happy with it. However, it is also quite expensive, and there is a quite some functionality, which I really don't use. A collague of mine is very happy with CLC Main Workbench, which has not been mentioned here. Both programs should be good if whole groups are working with it. As I understand it, the database use for a whole group is better in CLC, whereas manipulation of DNA for virtual cloning was better in VNTI - at least 2 years ago, when I last compared both programs (but CLC wanted to improve in this area). The service by CLC was excellent (I was told by my colleague), whereas my initial experience with VNTI was devastating. They have improved in handling requests, but couldn't really solve my last problem I had.
Of the freeware programs I also heard that GENtle should be good but never tried it on my own.
Since I initially was trained on the old GCG command line program, I agree to some extent with Christopher - always remember, these programs are way to visualize the plasmid, but when cloning you still have to do all the thinking on your own.
Finally. I would like to mention that addgene has a nice tool "analyze sequence" to automatically annotate a sequence with the standard elements of a vector (promoter etc). I haven't found this in any of the programs I used so far - but I am also far from being an expert.
I tried the WebDSV recommended by Vladimir Cermak and it is really nice. It is good for drawing plasmids with basic features. The downside is that it does not allow much formatting options. For a quick simple project, I think it is very good.
I used to use even a more friendly software called Plasm. Unfortunately, I cannot find links to this software anymore. Although it did not provide advanced options, yet it was very user friendly and the limited options provided were basically what you mostly need for a drawing. I would appreciate it if anyone can provide a link to such software.
ApE!!! (A Plasmid Editor) http://biologylabs.utah.edu/jorgensen/wayned/ape/
I've been using it fro years now.
It's free, light and powerful - what else can you ask for?
You can blast with it, align multiple sequences, add and modify restriction enzymes (RE), create personalized RE lists, translate sequences, find ORFs - in short: all your heart can desire.
Sapio Sciences Exemplar Electronic Lab Notebook (https://www.sapiosciences.com/electronic-lab-notebook-software-eln) bronze edition is free to academics and is a full featured ELN.