Teamviewer works very well.
Pocket Cloud works well for me.
If you want to stick with "standard" stuff, these two programs are the best I've used:
For RDP, iTap. It's easily the best RDP client for iOS that I've used (and it's even good on Mac OS X).
For VNC, iTeleport.
I've spent well over $100 on "remote desktop" apps on the App Store, and those two are the best I've used.
I use RDP for work, so I searched the App Store for RDP apps and nearly bought them all, so you can see how that would shoot into the triple digits, quick.