The accountant in me likes to make sure I have Ketel One around at all times. Great vodka, great price. Belvedere Intense is solid. I'm a big Chopin fan. Grey Goose is solid. But Ketel One is the one I always have on hand.
When I am putting together an online order, or I have someone able to buy for me and bring into their store, I like to try some more obscure brands.
If you haven't already, try Karlsson's Gold Vodka (made in NY). Very nice vodka, maybe $30-35/bottle. I found it after a wine magazine named it their best vodka (it was maybe Wine Enthusiast or Wine & Spirits??). Grand Teton Potato Vodka is also nice, and pretty inexpensive (I think I picked it up for like $18/bottle).
EDIT: I found the article that led me to Karlsson's. I didn't realize Grand Teton Potato Vodka also made it (so did Ketel One):
http://www.winemag.com/October-2013/Octobers-11-Best-Vodkas/