Dimdim.com is an excellent product for online conferencing and possibly for demos as well and its free for up to 20 users. Its also very easy to use.
I also think gotomeeting is a good product - I used it for numerous presentations and didn't see it as an unprofessional product. Sometimes the client software gets tangled up in the firewall configurations, though.
Can you provide some insight on what made you feel that gotomeeting was unprofessional?
Another good webinar / demo service is calliflower. They have a freemium model, and if you are running demos with 15+ members, it can be cheaper than many of the other services.
There is a no cost option - why not google docs? You can upload a powerpoint slide (or create a presentation online), invite people, schedule a conference call (http://freeconfreence.com can help out here) and then present to them using google docs (no presentation app download needed). That could either be interpreted as cheap or cutting edge.
Assuming you don't want to do a live demo, you can use Adobe Captivate and record a demonstration of the said product and then place it on your website.
There are also cheaper programs, like Camtasia Studio.
Our sales team is currently using WebEx and Live Meeting for live demos. We are actually dumping those next month and moving to GoToMeeting. The pricing model for GoToMeeting was better (meaning that we had more control over costs). Plus, we had a number of demo sessions with our sales team and took a survey on what package they would prefer. The result was unanimous. Everyone liked GoToMeeting. I'm the CTO and so I don't use it that much myself, but I didn't think that GoToMeeting was unprofessional or non-serious.
Anyway, it's just one team's opinion, but we liked it.
Might as well throw out the free program Wink
http://www.debugmode.com/wink/ It let's you do screen captures and recordings, then the program allows you to make notations and control the flow of the app.
I'm not sure what you mean by "non-serious". If it's image you are after, I'm surprised Gotomeeting isn't working out, but I'd second the advice for using WebEx or Live Meeting as alternative solutions that portray a more corporate feel.
DimDim is great, but has that "open source" / "free" website thing going on that may not present the image you want with your customer base. (Based again on your non-serious note).