WEEKLY-ICS you NEED to KNOW: Princeton PT2399:

Datasheet can be downloaded here: http://sound.westhost.com/pt2399.pdf

pt2399 pinout

This chip is used (and this is only from the top of my head) in : DOD delay pedal; Danelectro FabDelay; numerous other delay pedals, Synthrotek's Dev Delay, EKO module, EKO mkII, Cosmic Delay; GetLofi's Lo-Fi delay, Mad Bean pedal's Sparklehorse and other digital delays, the DIY-site ubiquitous Rebote Delay pedal, and on and on.

In other words-if you have a couple of hardware delays in your studio/music area, then you probably own a PT2399 at work.

There are a number of reasons for this:
-its a REALLY good self-contained, one-chip answer to audio delay.
-it doesnt require external memory like the MN-type analog BBD delays
-it doesnt require the 'dialing in' that other delays do, meaning you have to mess with a trimmer after
  building a circuit using it
-PT2399's can be CASCADED to increase delay time (time between returns)
-it allows you to add everything from Reverb to Chorus to a device with very little effort
-a fully-functional audio delay circuit can be made with it employing just a handful of passive components
-etc

Important DIY info:
There ARE onboard Op-Amps (meaning it can also do all the things opamps can do-simple synths, negative feedback amplification, etc) BUT about the heaviest load they can drive is roughly 1kohm (in my experience-I honestly dunno what the datasheet says if it says anything).

Always ALWAYS make sure the grounds are grounded: in particular, I am referring to Pin 4 (digital ground)--do NOT ignore it and assume since you have Pin 3 (Analog ground) grounded, you are OK. For a number of reasons, this is not so.  Most time, the easiest way to deal with this is to connect Pin 4 to Pin 3

Noise is something you are going to HAVE to deal with there just isn't a way to avoid some minimal noise with the chip..but normally that doesnt matter-especially when dealing with something like a guitar pedal where you can just chop the  output frequency at human-audible levels if necessary.  The normal way I deal with this is just to use a 7805-type regulator on the power and a 2.2uf (or less, whatever works for your purposes) decoupling capacitor.  After that, noise should be reduced to a easily handled level.  Just remember, if you design a device/circuit with the PT2399, do NOT leave out some means of dealing with noise simply on the assumption its digital and wont produce much

Modulation can be EASILY added -there are a LOT of different circuits and means of doing this, I dont want to say too much about it-just know it can be easily done and use your favorite search engine to figure out the way that works best for what you have in mind.

Its pretty easy on power -you wont have to worry too much about overall drain when you add a delay to your circuit via the PT2399-likely you will not need to alter your power in the circuit at all. For example, if you are using a 9v DC batter with a simple 78xx regulator and so forth for whatever you are already doing, you will not have to worry about drain if you add a PT2399 (thus adding delay) to the circuit.(in MOST cases)