The WotC Dungeon Delves book is a title that provides a full, three part experience (typically centered around three main conflicts) in a single location (with fully detailed maps and enemies) targeted at a specific level of characters. Regardless of your opinion on the idea behind the product, it's a great resource for DM's who need a quick, but interesting location or just need a bit of inspiration. Are there any books or websites dedicated to (or focusing on) dungeon delves?
The best delve resource I've found is here which is annoyingly impossible to find by searching. It's a list of every adventure published in DDI by level with a short summary. There's also 18 volumes of systemless well constructed delves here. Along with a delve-creation methodology that I've used quite successfully (the 5 room dungeon)
The Chaos Scar is an ongoing mini-campaign composed of about a dozen (so far) small adventures. You'll need DDI access to get everything. Each adventure can be dropped into any campaign with little prep without needing the full campaign. (I've used several this way.)
Goodman Games offers In Search of Adventure, which has 6 short first level adventures. I haven't played this one, but I've used several other Goodman Games adventures and can recommend them.
Monte Cook's DungeonADay.com does that but for 3.5e.
Tony Dowler's Year of the Dungeon blog provides a variety of "microdungeons" and other interesting locations, with minimal sketches and descriptive text. No crunch, but a lot of flavour.
Not quite delves, but http://dailyencounter.net/category/encounters/ has an excellent series of encounters presented with stats and tactical maps.
The folks at 4e Home Encounters state that they're going to be releasing encounters that are part of a larger story line, in the same vein as Wizards' Encounters program. Emphasis on "going to be" because they haven't released anything yet, as of this writing. Something to keep an eye on, though.