PNP Arcade - One of my favorite PNP shops. Has a wide range of free and paid PNP games organized by by player count, which is particularly useful to the solo gamer. Currently emphasises micro and card games as well as roll-and-writes.
Solitaire Games on Your Table Aggregator - The SGOYT Aggregator is an invaluable resource for the solo player. Enables easy searching of all past SGOYT threads to get playnotes. I have consulted it often.
Boardgamegeek - BGG is the defacto tabletop gaming community. I use this site a lot to share files, buy and trade games, and log plays, plus there are many geeklists and forums for discussion. It is home of the 1 Player Guild and Print and Play Guild. Many annual board game design contests are hosted here, including the Solitare PNP Contest, the 9-Card PNP Design Contest, and the Wargame PNP Contest, to name a few.
BGG Buddy - A stat app that links to your Boardgamegeek account. This is the easiest way I have found to sort games by the date they were last played.
Boardgameprices.com - Excellent way to get a quick idea of what a game is currently retailing for and how widely available it is.
Bored Gamer Tools - A BGG stat app that includes arbitrary challenges (Insights > Challenges)