Hi Jayne
Like Gadget and the others, I use the IGI first - it has the advantage of not requiring an exact name match, and it is free, but if I can't find the information on the IGI I head for ScotlandsPeople.
SP is by far the best genealogy site for any useful BDM information, but you do need to practise the search routines so as not to waste credits. You can search as many times as you like without paying - until you decide to view the results. I wasted credits learning how to search properly and now make sure I get a page full of useful results for each search, not just one line
The civil searching on the IGI has the advantage over SP in that parent names are on the birth records. It has the disadvantage that there are very few death records on the IGI.
A certificate costs £1.20 - definitely the cheapest I have ever found - consequently I have more certificates from Scotland than Australia & not many of my folks were in Scotland post 1855
If you can't find the folks you are searching for - post some messages, I'm sure you will get much help at RootsChat
Trish
Edit: You probably need to advise if you are looking pre or post civil registration - I find both types of searches quite different. The church records on SP are mainly church of Scotland records. If you folks belonged to other churches you may have difficulty finding any records in Scotland pre 1855