I know this isn't exactly a thrifty tip. Still, since so much is done in print and via email these days, avoiding even seemingly small misspellings and typos can make you more marketable in a tough economy. Attention to detail will set you above the crowd.
To know whether to use "stationary" or "stationery" in a sentence, use this simple mnemonic:
STATIONARY = You AREN'T moving
STATIONERY = PAPER.
Source: Seeing a misspelled instance reminded me of my English classes of long ago.
JustPlainJo, Springfield, Ohio