I've used Radmin, Ultra-VNC and RealVNC, all a matter of preference for me, I prefer using REALVNC, very easy to setup and utilise, although I must share a true story that gave me a wake-up call and made me much more security conscious.
Just last week I did a clean install on my laptop, installed the RealVNC server and viewer while installing my programs and forgot to setup the password. I was in the middle of installing Office when I noticed the RealVNC icon indicate 'presence', within a fraction of a second my "Run" bar was open and busy being typed into, I didn't see what was been typed as I immediately ended the session and setup my password and security. Lucky I was present when this happened as I would very much dislike to think what might have happened.
Yep - to add to that, RealVNC is not secure without any form of encryption. UVNC is my choice as you can create and use encryption keys, but even that is an issue if others have access to the server machine... reason being 1) just copy the key file and 2) get the encrypted password from the registry and decrypt it with the many tools freely available. That last bit is surprising - the VNC password is encrypted with 3DES AFAIK using a static encryption key, so is easy to crack with access to the registry.
In the days of Windoze 98, we used to get access to the c:\ drive over the LAN - it was common for lan admins to share the drive out of laziness, then copy the registry files from the windoze folder and strip the password there, then decrypt it. While staying at a local hotel, I got access to a managers computer and copied some choice words into the clipboard, then pasted them in the middle of the word doc he was in the process of typing - just a pity I didn't get to see his face lol...
I am more a white hat btw and learn security through curiosity and real world practice

My fav method of alerting people to open wlans is to print 100 pages to their shared printer with something like:
I will encrypt my Wireless access point
I will encrypt my Wireless access point
I will encrypt my Wireless access point
I will encrypt my Wireless access point
I will encrypt my Wireless access point
I will encrypt my Wireless access point
Toner may be expensive, but it's a small price to pay to have a free security evaluation on the most vulnerable part of your IT system. At least I wasn't like some people I know who used to print 999 pages in 100% black coverage and likely destroy the fuser unit of the printer in question.
If you do use VNC, go UltraVNC with encryption plugin and change the default port from 5900 / 5800 to something else, making it a little more difficult to guess/detect with a scanner.