Splashtop Remote Desktop is my choice. The free 'streamer' (server) runs on the PC, and the client is available for iphone, ipad, webos, android, playbook, kindle fire, nook, mac and pc.
On the plus side, it does video streaming better than a VNC connection, the clients
go on sale frequently, and (once purchased) the client can be used to connect to any streamer.
On the minus side, you have to buy each client (although non-commercial PC client use is free) and last time I checked, games needed to be run in a window.
Note that I haven't tested with a bluetooth keyboard, and that might be critical for excel purposes. Be sure to read some reviews before purchase.