Q: Is it possible to have a WebCombo with a drop-down suggesting values starting with the text entered in the textbox (similar to the example here: http://live.intersoftpt.com/cs/WebCombo/EntryMode_AutoComplete.aspx?noframe=1&path=/WebCombo/Top Features/Time-saving Combo Features)
A: The link is point to one of WebCombo feature called “AutoComplete entry mode”. To enable this feature, simply set the value of “EntryMode” property of WebCombo to “AutoComplete”.

Q: The list of options is retrieved from a class representing the business layer (no direct LINQ to SQL integration or similar).
A: We have a sample of WebCombo bind to ISDataSource control where the schema type of the data source is custom object. The sample name is BindCustomObject.aspx.

Q: The business logic layer receives as parameter the text typed in the textbox (so that the business layer does not have to query the database for all the items, but only for the items whose name starts with the string typed in textbox)
A: As Glenn answered to your post at following link, http://www.intersoftpt.com/Community/WebGrid/WebCombo-with-filtered-drop-down-behavior-and-business-layer-samples/, a sample for such scenario has been provided in the WebCombo sample LoadOnDemand.aspx. An article in the WebCombo documentation has also been provided for LoadOnDemand in the article titled “Load On Demand” and “How-to: Apply load on demand in WebCombo”.