The first two pics are by Scott Robertson [his blog is Here], and the third is by Mike Hill. The last image is a selection from the illustrative book called Battle Milk Volume 4, which is full of cool concept designs [it may be currently out of stock, so you'll have to search for it].
**EDIT: JULY 2011**
Here are some more ultramodern vehicles for you to behold, ranging from armored trucks to police hovercars. When you open the images and save them on your hard-drive, you'll see the name of the artist that created the pic, presented within the descriptive tag. I'll be doing an article based on Steampunk vehicles later, so watch this blog via Facebook , and keep an eye out for that post as well!
And Check out the Recent DSNG blog article on Hovercopters / Futuristic Helicopters and Hovercrafts, posted over Here.
Cool Links:
More details on the DSNG sci fi series, where hovercopters are frequently utilized: http://dsngsfm.blogspot.com/2011/06/exploring-dsng-part-11-usual-unusual.html
Blog Article on DSNG Chronicles book 4, plus sexy artwork: http://dsngsfm.blogspot.com/2011/05/overview-of-dsng-chronicles-book-4.html
Blog Article on Cheesecake art [if you're a geek, you'll love it]: http://dsngsfm.blogspot.com/2011/04/fanart-of-elena-eden-and-article-on.html