Theres also the mobile device management and mobile application management side of it all XenMobile and Appcontroller (now just XenMobile) and many other products;
As jfish says - Netscaler
Provisioning service (PVS)
Machine creation services (MCS)
Command Center - used to manage multiple Netscalers
Insight Services (used to be called TaaS / tools as a service i think) log file analysis via CDF monitor (Citrix diagnostic facility)
Other diagnostic facilityies - CDF trace, PVS data tools
Insight Center - Reporting
Director - new reporting
Edgesight - monitoring and reporting (now eol)
The big products are XenApp and XenDesktop though - delivering applications and/or virtual desktops to users. Prior to Xenapp it was called Presentation server, Metaframe, Winframe
XenApp/desktop often combines multiple of the above products such as Netscalers (you may hear them referred to as a CAG - citrix access gateway) a secure device which is a reverse proxy and used for many other things like load balancing, Web interface or storefront server(s) for enumerating the applications and desktops and XenApp and/or XenDesktop servers which the apps and desktops are hosted on.
Other things are thrown in the mix too like licence servers, STA (secure ticket authority) different types of reporting, group policy management packs like Citrix profile manager, logging and tracing tools, Hypervisors such as XenServer, VMware, HyperV, Provisioning services or machine creation services, Sharefile (Citrix version of dropbox) and many many other product offerings.
Citrix also offers public cloud based solutions, called something like Evergreen which is hosted on Microsoft Azure infrastructure
I work for a global company so to use most of the above but have limited knowledge in some areas as there is a LOT to learn. Thats the reason I enjoy it though, it would be boring if it was easy! At the moment I am focussing on the PVS side of things (streaming XenApp OS VMs using images) and Netscaler. Using PVS is fantastic to manage as uses versioning but brings issues with it as the OS is streamed it relies on network and storage to be 100% stable