I came up with more of these than I thought I could.

• Backing up (files)
• Baking
• Ballades
• Bananas
• Bandwidth
• Bargains
• Barnes & Noble
• Bash
• BBC
• Beginnings
• Being
• Binomial nomenclature
• Blogging
• Blood donation
• Bookmarks
• Books
• Bookstores
• Boot-loaders
• Boundaries
• Brainstorming
• Brass music
• Bread
• Brownies
• Browsers
• Buckets (collection)
• Butch
• Buying