In part because of the market dominance of their database program, ChessBase also has the best-known database as well. The next edition of their MegaDatabase will have approximately 68,500 annotated games. That's a good deal, obviously, especially if one thinks about how many books one would need to buy to get the same number of annotated games. (And never mind trying to replay all those games on a board - your hands will probably fall off by the time you reach the halfway point.)
So it's a good deal, but an even better deal, at least or especially if you also own a generic large database to go with it, is the new "Paramount Chess Database" from the Chess Informant. It includes all the games from the main section of the Chess Informant from the very first issue all the way through Informant 123, which came out earlier this year. In all, there are almost 114,000 games and game fragments (about 70,000 of the former and 44,000 of the latter; the game fragments start from move 1 and generally cut off once the theoretical significance is finished).
It isn't just the total number of annotated games that counts, however. In Mega there are 59 games annotated by Garry Kasparov; in Paramount, 630. Mega has 268 games annotated by Viswanathan Anand, while Paramount has 507. Vladimir Kramnik? 64 vs, 442. There are only ten games annotated by Bobby Fischer in the Paramount database, but guess what? That's ten more than you'll find in Mega. In fairness to Mega, they win the Magnus Carlsen sweepstakes 24-0, as in recent years fewer top players annotate their games for the Informant. That's not to say that current games aren't well annotated - they are - but more of it is being done by staff grandmasters, while they have elite players writing articles for them instead. There aren't any articles in the Paramount database, but as an historical record of the best chess since 1965 it's almost certainly the best resource you'll find.
Continuing the count, how about 372 games annotated by Mikhail Tal (none in Mega), 17 games by Boris Spassky (two in Mega), 510 by Tigran Petrosian (the world champion, not his living grandmaster namesake; there are three in Mega), 29 to 0 for Mikhail Botvinnik, 55 to 5 for Veselin Topalov, etc.
It's a fine resource, but do remember that the annotations are given with the Informant's languageless symbols. It is a rich "language" in its own right, but lower-rated and less experienced players might find it a little forbidding at first. The Informant has generally been aimed at strong club players and up, so while I think players under 1800 can find this product useful as well, it is to players at and above that rating that I would offer my (hearty) recommendation.
The price is $199; a fair chunk of change, but very reasonable for what you're getting. (Think of how many books you'd need to buy to get your paws on 114,000 games.) To my mind it's a very good deal for serious players, fans of chess history and for correspondence players, so if you're in those categories you have my recommendation.
More info at the link above (reiterated here), including a nice video that gives you a tour of the product.