TI-83 is great if you really know it. You really don't need any more than that to get an 800. TI-84 what most people I know use, although there are definitely some 89 and nSpire users as well. 89 and nSpire are quite a bit more complicated to learn then 83/84 though they are also considerably more powerful. You can try an 89/nSpire if you've got the time to figure it out though.