For Links to almost anything you could ever wish to view and read about Scotland, visit Rampant Scotland. Despite the graphics, it is a really comprehensive index of Scottish Life.
In the last two hundred years, there have been a lot of marriages between Chisholms and Forbes. Information on Forbes and many other Highland Clans/Families can be found at "The Gathering of the Clans". Including a very confused page on the Clan Chisholm which mixes up the Highland and Lowland branches. It also hosts a discussion group for Chisholms.
For another brief page on the Clan Chisholm, take a gander at Sgian Dhu Interactive.
Roger Chisholm-Batten has an interesting site and has taken the Geneallogical Charts drawn up by Wilfred Medlam and has converted the Chief's Line to a series of pages which can be searched and viewed. One warning to anyone browsing pages relating to the Chief's Line. If you are familiar with the Chief's Line family tree in Jean Dunlop's book then you should be aware that the tree from the book at around the time of the '45 appears to have been simplified.