bear and bare
"Bear" and "bare" are often mixed up when people write that they can’t bear/bare another minute of something. To bear something is to carry it. To be bare means to be unclothed and unshod or, like "bare" wood, unfinished.
classic and classical
As a noun, a "classic" is an important – and perhaps even influential – example, while as an adjective "classic" implies adhering to a standard of excellence. Technically speaking, "classical" has a narrow definition, describing things from ancient Greece or Rome, things from analogous ancient periods like the Tang dynasty, and formal concert music of any period. Except by the picayune, today classical is used to describe things of authority and excellence.
a while and awhile
"A while" means “a period of time”; "awhile" means “for a time” (when "for" is included, you’d never write "for awhile" because in essence you’d be writing "for for a while").
etc. and et al.
An abbreviation of et alii (“and others”), "et al." refers to people; "etc.," an abbreviation of et cetera (“and other things”), refers to things only.