Advisor vs. Adviser
Not to argue something trivial, but I’ve always personally used the spelling advisor. Since adviser looked awkward, I decided to investigate. My research indicates that the two terms are interchangeable and neither can actually be deemed incorrect. See the web definitions of advisor and adviser.
Merriam Webster says the words are synonymous, as does the American Heritage Dictionary, the Random House Unabridged Dictionary, Roget’s Thesaurus, and Princeton’s WordNet. The Purdue Marketing Communications Editorial Style Guide insists on the spelling advisor over adviser. The Columbia Guide to Standard American English states that “both spellings are standard”. It does not appear that the agentive ending –er or –or has any semantic meaning in the case of either term.
Furthermore, a Google search for advisor returns 85,100,000 pages, while a Google search for adviser only returns 21,500,000 pages. This indicates that, at least in common usage, advisor is dominant at a ratio of four-to-one overadviser. It is also argued that the –or version is aesthetically pleasing in comparison to the –er version.
While neither are technically correct nor incorrect, I prefer to use advisor. *shrug*