I like the guides from Gamespot, especially some of the ones for older games like Baldur's Gate which are downloadable PDFs. I subscribe to GS so I have access to all their guides and if they don't have it, there is always gamefaqs, Google, etc.
On some special occasions I will get a print guide. I have one for Morrowind which covers the expansions too. It's a fun guide to peruse and find quests and other things I missed, details on character creation choices and more. I am planning to replay the game sometime soon where I never did the main quest nor the expansions when played it in the past. A refresher on the stats, choices in character creation, etc. will be cool. I am the kind to spend a while reading about a game before I dive in. The Gamespot Baldur's Gate guide was great pre-game reading because it taught me about AD&D rules governing the game and about character creation and the importance of the various stats, abilities of various classes, etc. In a way both these guides just mentioned here contributed to fun for me. I liked starting off with some idea of what I was doing.
Not too long ago (I think there must have been a big sale) I bought all the Sierra adventure games on GOG and I know I will sometimes get stuck in these for sure. So I went on Amazon.com and was able to find at cheap to reasonable prices the original print guides for each of these series: King's Quest, Space Quest, Quest for Glory and Police Quest. These will make the games more fun for me since i can easily get help if I get stuck.
Once I realized I could find guides for good old games on Amazon.com I went on a bit of a spending spree. I found guides for The Ultima Collection and Ultima IX so I have that entire series covered. Then I did the same for the Might and Magic RPG series of games. Lastly, since I am brand new to turn based strategy games and own the Might and Magic ones, I got the guides for the first, second and third games in the series. I figure they will be fun to have and get me off to a good start. I have played a bit of the first Might and Magic strategy game and I really liked it. So I'm sure I'll put these guides to use over time.
All those are the first time I've bought a printed guide since I got the Morrowind one quite a long time ago now. I wouldn't attempt to buy a guide for every game I own nor do I think it necessary but for those good old games I just couldn't resist getting good old guides too.