I have not walked into a Blockbuster or Hollywood video for ages so I have no idea if they rent consoles anymore.
I think your best bet is to go to a Funcoland or some other used game store that will let you try out a game before you buy it.
The alternative is to take my word that the XBOX360 simply rocks and is worth the purchase price (especially if you are willing to pay for Xbox Live).
Chromehounds, Dead Rising, Street Fighter II, Oblivion for released titles and certain exclusives like Gears of War/Halo 3 makes the console a worthwhile purchase so if you can afford it - don't beat around the bush and buy the console.
Jam it back in, in the dark.