Big fan of Logmein. It's pricey for iPad client, but works great. And unlike you heard in this thread, there's NO extra payment required for it. Ever. Yes, you can upgrade to Logmein Pro 2, which is $70 a year, but the features it offers are pointless on iPad. Free version gives you file transfer, and I believe, printing.
Another reason I love Logmein is that it supports 2 factor authentication, and does not need ANY firewall/router configuration. My Logmein account has about 700 hosts. If I had to setup a router for each one of them and then deal with Dynamic DNS (service that does cost money), and re-setup routers once customer replaces his Linksys with Netgear or something, I flip.