Also I wanted to state the obvious cold books:
Any book that has these stupid variant covers to them. They are all fad in my opinion and will lose significance over time because every single book now has about 5 or 6 different covers. Mainly the Batman series. These little ComicCon variants are all just hype. I wasted a lot of my money on them only for it to equal about half of its worth compared to the 1st release.
From my studies on comic books, they gain value by one of 4 categories:
1. Age
2. Significance
3. Rarity
4. Appeal/Cover
The more appeal it has in each category, the higher the value over time. Cover alone without significance to the story (ex: Batman Sketch Cover) is simply fad. People will flock to it because of "rarity", but in due time, it will greatly lose its significance. I rarely shoot out cash for CGCs that are not 1st appearances or some extreme significance. Golden Age Batman ex: Classic Joker Covers = extremely larger significance than some simply Batman and Robin riding a tricycle. The Batman (I think it's 29) only has value due to its age and being within the top 30 issues of Batman. It may go for about $420 at a 6.0, but it took over 60 years to get there. The modern age 1st appearances such as Carnage have great significance and will only gain value with age. Today's moderns are future Bronzes and Silvers, etc. Great investments.
P.S. Sorry about the extreme ramble. Most of you probably already realize this. However, I take medication that makes me hyper and crazy