depends on how much you have to spend.
the BG-E3 mattery grip is a must have for the xt (which will also lead you to needing to purchase an extra battery) i think it runs around $150
if you dont have much to spend, you may want to look into a tripod. another must have accessory. you can find a cheap one for like $20-60. i believe i payed about $160 for mine.
if you want to jump straight into some glass, id suggest a 50mm f/1.8, which will run you around $70-80. great prime lense for youre collection. theres is also a f/1.4 and a f/1.2L. but they will run you quite a bit more for them.