A Standard size phalaenopsis is perfect for your choice and it's readily available in the big box stores especially Lowe's. Some novelty phalaenopsis is very tiny that it can fit in a vivarium making it a good candidate too, like this:
Phal. I-Hsin Spot Eagle 'Montclair' IN SPIKE: Orchids By Hausermann. Generally, Phalaenopsis are long lasting and easy to grow and fit an Eastern window.
About big showy flower, nothing can beat a floofy catt. An example could be the big famous Blc. Chia Lin is recommended for color, substance, fragrance, neat growing habit and ease of culture:
Flickr: Search. Needs very bright light though.
Oncidiums are good choices too. Sharry Baby (chocolate orchid), Sweet Sugar (yellow dancing lady orchid) are easy to grow and need medium light. (do not choose the Miltoniopsis!)
Maudiae Paphiopedilum is good because it's long lasting; the vinicolor and coloratum variation are showier than alba:
http://www.orchidboard.com/community...hp?photo=15480. These flower can have pretty decent size. Some delenatii crosses have showy flower on compact plants but last for only about a week or so.
I have this guy:
http://www.orchidweb.com/detail.aspx?ID=1949
Easy to grow plant with big flower and long stalk and it looks very pretty with some burgundy color on the leaf.