I could quote and link to the countless pages and pages that go on and on about copyright laws in regards to digital media (I found this very page while looking into laws about screenshots). (Strange how nobody seems to be a lawyer on the Internet.) However those are easy enough to find and moreover, most of them just reiterate and copy-paste the same basic information about fair-use and general requirements and usually end up vague and essentially say that it depends on the specific circumstances.
Instead, I’ll explain what is likely (based on what you have mentioned) to be the case in your situation.
GameSpot (which like TV.com is owned by CBS) makes a point of blocking the posting of any images for which written permission is not obtained, but then again, it is big site, generating revenue.
No sane person would expect for no fan-sites to be made of their product or even to expect that all fan-sites pay for permission to exist. Further, no rational person would expect a fan-site to use only plain text for everything. They may expect you to create your own images, but that is extremely unlikely since anybody that foolish would likely just end up being the kind of person to sue for plagiarism of their images and even for using the names and stories they created.
As such, it is expected that fan-sites would use images of the game/show/etc., but of course, within reason. In your case, using cropped images for avatars or links is highly unlikely to draw the ire of anyone, especially since it is still a small site in the making. It would not likely be impinging on any of their rights or costing them current or future monies, so they would not care and in fact probably be happy for the added exposure.
If your site manages to become huge (think Facebook), then they may try to demand money for permission to use images of their games (i.e., to make the site at all). Of course if that were the case, then you would likely have the money and staff to do so, so no worries.
But even if your site becomes very successful, it is more likely that they will instead just demand that you get written permission and credit them for the pictures (e.g., a copyright or permission notice, link, etc.) Of course you can already implement attribution on your own up front; that way they may not even demand you obtain written permission since you have already provided them with the credit they expect.
Also, don’t forget that because you are presumably dealing with multiple games, you will thus (potentially) be dealing with multiple companies/law-firms, which means that they will probably react differently. Most will probably leave you alone, and the few that bother you can probably be easily dealt with in several different ways (gaining permission, replacing them, or in an extreme case, removing them altogether—and maybe adding a punitive message as to why that game is not included.)
(I never really understood attribution/credit in this regard since nobody is going to think that the authors of the blog are the ones who created the game/movie/etc. in question. Anybody who visits fan-sites is going to know who the author of the original work is. Duh. They may however like a link since links are one of the currencies of the Internet.)