Are you talking about the username and Password to log into the router? If so, the defaults can be found on the manufacturers websites in the PDF user manuals, or in the hard copy user manual that came in the box.
If you just forgot your username and password, after you changed them, just use the reset button on the router (almost all of them have a reset button that needs to be depressed with a paperclip or something similar).
That resets the router to the factory settings. You will have to set it up again, but worth it for a forgotten password sometimes.
I use LogMeIn and I tell you, no problems what so ever. The app is pricey but I've had nothing but ease of use for the money.
Straight up remote control of your computers. You buy the app and then you go to their website and sign up. There is a free option that you download to your computer follow the instructions...and then do your test log in from your iPhone.
If you have domains on your computers the key is to remember which one you left on and remembering the domain correctly. The iPhone app will allow you to save many computers with various domains and logins.
I love the product so much I actually bought a year subscription (after finding a great online coupon) for the mega super duper hookup. I have 2 computers on it one free, one with a paid subscription that I use the most for meetings and such.
I often use my iphone to access my work computer from the airplane to kick off long running processes late in the day on Thursday after I know everyone is gone. That way when I work from home on Friday the processes are already done.
I will admit, I wouldn't use the iPhone app for typing much stuff or doing anything that requires a lot of typing because it is a pain in the arse. But for navigating files, viewing stuff, kicking stuff off, printing stuff etc it is excellent.