I am sure there are others on this site that can give you good advice, but here's my 2 cents as a multi-time visitor.
I love the Highlands and north/west Scotland!! So, since you plan to hit Loch Ness perhaps you can consider some other things worth hitting (please refer to map or guidebook for details):
Loch Lomond -the bonnie, bonnie banks...
Oban - nice little seaside town
Glen Coe - great scenery
Fort William - cool little town, not far from Ben Nevis
Isle of Skye
- must-do! hike around the Quariang - awesome/other worldly!!!
- the Cuillen Mtns are also pretty stunning
The Road to the Isle of Skye, Kyle Lochalsh
- Great scenery, lochs and Eileen Donan Castle
While in Glasgow area, you readily can swing down to Ayre and Alloway (Burns country)
Not sure how much time you will have in the country, but the whisky trail is nice. Even if you cannot do this, there are distilleries with tours all over the place (Talkisker on Skye, Oban by Oban, to name two).
In Edinburgh, there's a ton to see, which I am sure you're guide book will help you. Walk up to Calton Hill and get some photo's of the city, Arthur's seat, etc.
Some of the smallish towns south of Edinburgh are nice (Moffit, Selkirk, Falkirk, Melrose, Jedburgh, Kelso, etc.)
Obviously, St Andrews on the east coast is not so far from Edinburgh to the north, if you are into golf.
Below are a couple links
http://www.toscotland.com/
http://www.visitscotland.com/
I could go on and on about various spots, castles, etc. but I'll trust you'll see locations of those in your guide books.
So, I hope you enjoy the most spectacular scenery in the world, one-way roads, bald heathery mountains, lochs and sheeeeeeeep!!!
I am jealous of your trip!!!!!
