I've heard a lot of good things about various text-automation apps, but I'm personally partial to AutoHotKey. It does the same things as the others, and the scripting language is very powerful. I use it to autotext most of my email at work, and to hotkey various websites I have to access there.

Since I do customer-service work some of the time, most of the abbreviations I use go to that:

• cm == customer
• cuc == customer called to
• unp == text block of a request to various warehouses to unpick products from shipping lists so I can modify orders
• cd == "customer data" text block of customer demographics
• ]d == current date/time

And so on.