I'll throw in a vote for LogMeIn - I've been using it for about 5 years, and it's been great. The iPad app is great as well, and I grabbed it a few months ago when they were running a special and offering it for free.

LogMeIn unfortunately has started removing some features from their free version, like the Desktop Shortcut (where you could create a shortcut that would take you directly to a particular machine on your account). I loved this feature and had shortcuts for my most frequently accessed machines, but they've taken away that feature from their free version