I've been designing with 3-lead through-hole ceramic resonators, but I'm looking to try surface-mount crystals, but I'm having some trouble. I'm looking at 4-pad packages like this one, which have two ground pads. What I can't figure out is if these packages have built-in capacitors connected to these ground pads like the center lead of the resonators I've been using, or if I need external capacitors. Also, all of the eagle parts I can find with these 4-pad configurations don't allow me to connect the extra pads to anything. Does anyone have experience with these crystal packages? Recommend a library?
Well the data sheet that spark fun has for this crystal shows terminals one and three are the crystal terminals and two and four are connections to the devices's case for connecting to ground. So you will still need two caps wired from one and three to ground.
See section 3 of the data sheet:
Lefty
It's a crystal just like the 2 lead packages on the standard arduino. It needs caps.
If you look on page 3, it indicates the crystal is attached to pins 1 and 3. Pins 2 and 4 are just mechanical connections. (Boy, that's one ugly data sheet!)
To complicate matters a bit further, there are devices called oscillators that have 4 pins (3 of which are usually used). They don't seem to be used much anymore. They need 5V, GND, and put out a TTL level square wave at the indicated frequency. While they are not replacements for crystals, many microcontrollers can use them in place of crystals.
-j
i use these crystals , only 2 pads. You need caps. carefull with soldering 
i have problems with that / in case i use homemade reflow oven with perfect profile/ with solder iron is little more dificult.
regards