Woah you're lucky that you have such a big budget sponsored by your sister... In terms of models for the Canon and Nikon ones the last few in the list (meaning the 300s/700 for Nikon and the 7D/5DMk II) are the most expensive. They are also hence the better models (that too is also quite disputable). However, as some of the people here have posted, there are 2 things you must note:hi,for below mention,which model are best?
budget can increase if not enough,because sponsor by my sis...
1) It is best to go to the shops and try out the models yourself, it is hard for people to give you a direct 'I think this is the best', especially between camera brands because people have their personal preferences and reasons for choosing a specific brand (say a Nikon over a Canon) and within brands a model over another (Say a 7D over a 5D MK II), hence the best thing to do is to set aside time for 1-2 days and go down to the shops and just try out the different models for yourself and decide what suits you best.
2) I agree with one of the posts here though that regardless of how big your budget is and how much you have free to spend, photography is not cheap, and if you are new you should ask yourself if you really want to be serious and really use your camera heavily. If you have that passion and want to get really serious, FX Cameras like the D700 and 5D MK II are for you, but they cost a lot more. However, if you are more into it recreationally, you might want to start smaller with models like the D90/D300. I think the point I personally am driving at here is that even though you have the budget to buy the most expensive, you may not need/use some of the functions they have as yet.
Besides, if you have the ability to afford the best, upgrading later hopefully won't be a problem for you
Just my two cents worth!