It's well known that programmers don't do art (except for a very talented few): more often than not, we end up with either bad code or programmer art. However, there are many great resources to get assets for your title, even if they are only placeholders until you find a designer who is worthy of your vision. The following are some of the best places to start your journey from:
One of the latest marketplaces to spring up plenty of assets is the new GameDev Market. It is chock-full of 2D, 3D, textures, and even sample GUI art of which some are paid and some free. If you wish, you can also sell your own assets. The store is available at https://www.gamedevmarket.net/.
If free art helps you begin your title (sometimes even finish it), then one of the biggest sites is the OpenGameArt site. It has hordes of free-to-use assets, from spritesheets to textures and even audio, and it is available at http://opengameart.org/.
The VG resource is a forum-based art system where you can download or even request art and SFX. It is well worth a look (so long as you wear shades) and is available at http://www.vg-resource.com/.
Another source of freely available assets under a creative commons license is the aptly named search site, http://search.creativecommons.org/.
As we had an entire chapter in this title where we worked with maps, it only seems fair to point out this free resource for maps at http://freefantasymaps.org/.
A good review of some of the other most common map solutions out there for titles can be found at http://nevermetpress.com/six-rpg-map-making-solutions-for-your-game#.U6V1LvldURq.
Inspiration is hard to come by at times, so the following sites are well worth browsing for the next big idea (some assets can be used, just check the license):
If you are looking for some cool effects, visit http://dm4331-sidm-s1-2012-06.blogspot.co.uk/2012/07/updates-for-healing-and-fire-effects.html. I used assets from this site for the blood splatter effects in Chapter 9, Getting Ready to Fight.
Finally, sometimes projects don't go well and sometimes they die. However, if you are like these guys, you can share your content from your title. The following two links contain gigs of assets from http://www.glitchthegame.com/, which met its demise; however, the authors of these links gave all the game assets away for free: