I have quite a few, too, mostly Nintendo Power's own.
Back in 1990, the year before I subscribed, Nintendo Power, then bimonthly, planned to release six Strategy Guides (capitalization deliberate) in the months that a regular issue wasn't released. They only ended up making four reaching until the end of that year (as you can see in my Nintendo Power topic), one of which I ordered a back issue of...Super Mario Bros. 3. At the time, it seemed like it was the best guide ever. After those four, they didn't do any more of these Strategy Guides (which actually fit into the issue numbering), and Nintendo Power simply became monthly in 1991 onwards, and that's when I started subscribing.
Then a couple years later, I'm going to guess it was 1992, Nintendo Power returned to a similar idea by promising a number of Player's Guides with yearly subscriptions. The first four that all subscribers got that year were not specific to a game...The NES Atlas (just like it sounds...such a great book!), Game Boy (a look at various Game Boy games), Mario Mania (about a bunch of things relating to Mario, but the majority of it was a Super Mario World guide), and Super NES (a good look at then-still-new Super NES games). These are among my favorite books (of any kind) of all time. I think any retro gamer should have these in their collection. Soon after, they made a fifth Player's Guide, Top Secret Passwords (which covered a whole lot of NES, Super NES, and Game Boy games that use passwords, still somewhat common at the time but no doubt dwindling). While they didn't continue to offer an actual number of guides that defaulted to all subscribers, from then on they would often make getting the choice of one free guide as a yearly renewal bonus.
When they began with The Legend Of Zelda: A Link To The Past, the guides became specific to a game (Mario Mania, which covered Super Mario World, was practically there). I absolutely love this Player's Guide. Aside from the fact that it is probably my favorite video game, if you were to take a look, you'd be wowed by the amount of work put into this guide. It has tons of artwork not seen anywhere else, and really expands the world of Zelda with a lot of interesting facts and such (that no one's really going to debate are canon or not). Look at the Super Metroid Player's Guide, same deal there. So awesome. And despite beating EarthBound on a rental, I went and bought the game (at Canadian Tire for a whopping $100, which is a lot of money when I was still a kid with an allowance). Why? Because that game came with a Player's Guide instead of a regular manual, and around that point I had EVERY Player's Guide released. The EarthBound guide is so awesome because it came with so much artwork, including images of clay versions of various characters, and lots of amusing articles that showcased the offbeat and wacky humour that EarthBound is known for. Extremely well-done. My copy still has unscratched "scratch-and-sniff" cards in the back. Among the non-Super NES games, I loved the Link's Awakening Player's Guide too, for my only Game Boy game for a long time.
Unfortunately, something happened. I think it was around when I got the Donkey Kong Country Player's Guide. While still a valuable guide with all the maps and locations and information and stuff, it just felt like there was less heart and effort put into them. Pages were adorned with all that prerendered stuff, the cover was bland (just a close-up of DK's front on a white background...really?). There were still some great guides...take Killer Instinct, for example, that's a crazy amount of information. But I soon didn't feel obligated to get every guide ever, and, the Nintendo fanboy that I was, couldn't understand at the time why games like Final Fantasy III (VI) were getting the Nintendo Power Player's Guide treatment, which I thought should only have been reserved for Nintendo's own games (though now I am curious as to if they feature as much official art and the like, or if they managed to work closely with Squaresoft in this case to actually do so). But things were definitely downhill. The only N64 guides I got were for StarFox 64 and Pokémon Snap, which I only got 'cause I couldn't think of what preorder bonuses to get, and they just didn't seem as charming as the any of the Super NES ones. N64-era polygonal characters look kinda weird when you cut them away from a TV screen and you get this clipart of something with blurred textures yet with jaggy edges which are very evident when on a page and out of context. The Pokémon Gold/Silver Versions Player's Guide was good, but there's something very, very wrong with it. How do you make a guide - about a game that's about catching creatures - and you can't be bothered to have an index section showing all the details of every one of them?
And that's what I miss about Nintendo Power Player's Guides. Gorgeous artwork and vital information.
I'm a Nintendo fan, but I don't limit myself to just their games. A couple years ago, a friend gave me his PS2. I played some Square-Enix games on there, along with the BradyGames guides. I actually finished Final Fantasy X-2 maybe a month ago, and I admit to using the guide for that. Those are very thorough when it comes to the Final Fantasy titles on the PS2. I also have the Kingdom Hearts II guide, but I haven't really looked at it much, since I'd already finished the game before I bought the guide bundled with others for cheap. Oh yeah, and while I worked at Playdium, playing the crap out of Soul Calibur II in the arcade (I got over 10000 wins on my Nightmare character named "VGMAPS.COM" in Conquest mode...a mode like Risk that stores your progress in the game via passwords that unfortunately didn't appear in any home version), someone left a Soul Calibur II guide in the Playdium Sports Bar upstairs. No one claimed it for a month, so I laid claim to it. I'd have to check, but I'm guessing it's BradyGames as well, and it came with a soundtrack CD, and some great official art.
Maybe Nintendo Power dropped the ball, which is kind of sad as their very magazine probably started the whole "map-a-game-and-explain-tons-of-strategies". If not for Nintendo Power, I probably wouldn't've heard of games like DinoCity or Xardion. Maybe they're not the greatest games ever... But I recall there's a joy in seeing a game for the first time and suddenly knowing tons about it. I really miss that.