Hi Jeff,joining your local family history society is a good money saver.Mine is £12.50 per year and I can go 4 days a week and search through Ancestry for free,and any of the other websites already mentioned-and it's a lot quicker on their computers too!!
Using the UKbmd sites is a good tip-if you find a marriage you are looking for,you can get a print from the parish registers for abot 50p,it's exactly the same as the one on fancy green paper for £7 or £8.50 if you order from Southport + don't have a bank account! If it's not in your area,ask on here if anyone can get the info for you.
If you do send off for certificates,try to send off to local register offices where possible-the office in the registration district.They will check against other info you provide,say there are 2 Mary Smiths,born in the same quarter,tell them her fathers name and any other info and they will issue the correct one,if they're both wrong,you'll get your £7 back.If you use the GRO refs and order from Southport-they'll just issue it.
Local offices can't do marriages unless you have the correct church,though.
Good Luck,Andrea