The following photo from left to right, shows the following transceiver styles;
Xenpak2, XFP and a mix of optic SFP/SFP+ interfaces adapters
NOTE: The Xenpak2 ( aka X2 ) are the 2nd generation of the Xenpak. A Xenpak was support by a few linecard in the CRS , 6500/7600, and then Xenpak2 (aka X2 ) within the 4500/4900//6500/7600 series of cisco devices and is much shorter than than a Xenpak physically. Don't confuse the two. Both take a SC fiber connector, the SFP+ is used where the requirement exists for >4gbps interfaces.
NOTE: SFP+ is a enhancement to the SFP and offer data rates up to 11 gbps ( 10gbps optics actually runs closer to 11gbps due to line encoding ). A SFP and SFP+ are physically the same size but not all devices supports a SFP+ and 10gig line rate. Both takes a LC type of fiber connector.
Copper SFP various types
Their also few other interface such as CFP & CXP, which is primarily used for 40/100Gbps interfaces. It's much wider in size and only the top carrier grade equipment offers interfaces for CFP or CXP. You will not see too much of these types.
Most of these optics and transceivers are made overseas & with finisar being the most common manufacture. You can find more about finisar at http://www.finisar.com/
BTW, if you interested in buying the domains 40/100/1000 gige.net/com, I have this domains available for sale.
Both the 40/100 gige-based interfaces are becoming more and more available, and is what the future holds. Contact me for more information, or to make an offer for these domains.