An excellent genealogy search tool (explanation for good to excellent results follows the links)

INTERNATIONAL GENEALOGICAL INDEX at:

http://www.familysearch.org/

First of all, there are two kinds of records in the IGI--those from controlled extractions and those from private submissions. However, one can easily tell which is which. When you see an individual record with a batch number (bottom left of the record) consisting of six letters preceded by either of the letters C, J or K, you have a baptism taken from a controlled extraction. Six digits preceded by the letter M or E indicate marriages from controlled extractions.

Six digits preceded by P indicates that the record is from
transcripts of the parish records.

Beware of six digits preceded by the letters A or F--these are private submissions. Similarly, a batch number consisting of a string of numbers without a preceding letter are also private submissions. Just a film number will also likely be a private sub.

Beware of all births and deaths found in the IGI--parish records weren't usually concerned with births and deaths. The occasional rector did note these but only attached to baptisms and burials.

Beware of any bit of information that is bracketed thus . These are 'guestimates' and one will see names, dates and places with this designation. You may know that if church members found a marriage for a couple but not their baptisms, they were permitted to subtract 25 years from the marriage date to arrive at a probable birth date for the male, 21 years for the female. (You do that a couple of times in succession, and you can end up very wrong
indeed!)

Be very wary of anything that you find in the Ancestral File--very dodgy. Likewise with those new pedigree files that are now on line.

Now, once you have a 'controlled extraction' batch number attached to a surname you're interested in, you look for more of the name in that place.

Make sure you're in the IGI. Type in just the surname. Ignore first names at this point, and parents' names. Fill in the three 'location' fields, then type in your batch number in the appropriate place. Press Search.

If there are more with your surname there, you should see them now.

There's a good trick that you can do at this point to see if there are any more. If the church is a very large one or of a very old foundation, there may well be more of your people in those records.

To get at them, try changing the last digit of your batch number from, say, 1 to 2, then to 3, etc. This should get you more of your people if they are in there. (Some churches were so old and large--some of the ancient city churches, for instance--that more than one series of batch numbers have been necessary--see the end of this for the URL for finding batch numbers.)

Now using that same batch number but changing the initial letter to M, do the same thing all over again--this should bring you the marriages.

Baptisms will give you the names of parents or, in the earlier records, just the father's name. Marriages will give you the name of the spouse. (You can then start looking for those wives and mothers!)

If you find a set of likely parents, you can now utilize the IGI criteria page to see if those parents had more children--some could show up in a contiguous parish, for instance. 

Ignore the 'personal' name fields, fill in the father's name, first and last, and the mother's first name only. Fill in the location boxes, and press Search. (If you get too specific about filling in some of these fields, you'll may only get what you ask for and might miss records where a father's middle name has been omitted from the original record. Rectors could be notoriously sloppy at times.)

You can also use the year and year range filter if you're looking for a specific person.

To find out if a particular church you're interested in has had its records included in the IGI, you can go to this site and find out:
http://www.geocities.com/Heartland/Trail/8333/index4.html  

Here you'll find a list of counties, then an alphabetical list of all places/parishes within that county which have batch numbers and, of course, the numbers.

Remember that there are records of thousands of parishes in Salt Lake City that have not yet made it into the IGI and you can find these in the Fam. Hist. Lib. Catalog.

Further note, compliments of Roy Stickwell , Editor, the Journal of One-Name Studies (Winner of the Elizabeth Simpson Award for the most outstanding genealogical journal of 2000)

There is a further trick using batch numbers that I have publicised here before, but I will mention it again: if you enter just a batch number and a region and NOTHING ELSE at all - leaving even the surname field blank and leaving the Event and Country fields set to the default of "All" - you will find you can get the entire register, up to a maximum of 5,000 entries, from which the entries have been extracted. You can then scroll through the whole lot in screens of 200 at a time. It's time-consuming, but the advantage of this search method is that because of the peculiar way in which the Mormon standardised surnames table works you may spot an ancestor "lurking" in an obscure variant of the surname that you hadn't thought of before and which didn't show under a normal search. It may be you will find an ancestor hiding under a "unique" surname which you will recognise as actually being a misspelt variant of the name you are looking for.