Stu Maschitz reminded everyone in a Twitter note about his 2006 post A Tale of Three Blurs, which champions Box Blur in After Effects. Box Blur is adaptable with a "Repeat Edge Pixels" option and iteration controller. It approximates a Gaussian blur with 3 iterations, though Blur Radius might be lower (like 2) than Gaussian Bluriness (like 5). Iterations only works in whole numbers; you might need to gear down with the Ctl/Com key to get fine control over Blur Radius.
If you want more on blurs, Chris and Trish Meyer have 17 movies on feature pro & cons of the Blur filter category in their Lynda.com series After Effects: Insight into Effects.
Update: There's more on blurs in Blur 100: Introduction to Blurs a video by Vfx Hauiku. He doesn't talk about Frischluft Lenscare, an AE filter used by many power users.