Many of the moms on this board come looking for weaning tips at some point. Even families that practice child led weaning often need to set limits as the child ages and the nursing relationship progresses!  Here are some tips for those in need:
 
There are two great books that have advice on weaning toddlers/preschoolers.  The first is called
How Weaning Happens by Diane Bengson.  This book discusses different stages/ages for babies and children and gives support and age appropriate tips on breastfeeding and weaning.  It also gives a lot of detail on the differences between gentle mother led weaning, child led weaning, etc.  Mothering Your Nursing Toddler by Norma J. Bumgarner also has a helpful section on weaning towards the end of the book. 
 
Night Weaning
Oftentimes, night weaning can be a good way to extend your nursing relationship.  If your child is over one year old and is nursing multiple times a night, it can really drain your resources.  Many moms find that by eliminating nighttime nursing and thus giving themselves and baby/child a nursing free time it rejuvenates them enough to continue their daytime nursing relationship longer, rather than getting "burned out" on nursing.  This may not be the right decision for everyone, but it does help a lot of families.  There are many different ways to go about nightime weaning, so if you don't believe in CIO, don't worry!  Getting dad involved in calming baby during nighttime awakenings can help for a lot of families.  In other families, this may not work so well, or may not be possible.  Offering the child a drink of water when they wake up instead of nursing can help.  Some babies may need to be snuggled with until they go back to sleep, others may just get more angry if you try to cuddle them without nursing.  It is different for each family and child.  Dr. Jay Gordon's method of nighttime weaning in the family bed has worked for many families on this board (even those who are not cosleeping) and can be adjusted to what is most suitable for your family and child.    http://www.drjaygordon.com/development/ap/sleep.asp
 
 
Gentle Mother-led Weaning
It is best to eliminate ONE session at a time if possible.  It is just too hard on both you and your nursling to try to do too much at once, and you're much more likely to give in and have setbacks that way.  I'd start by figuring out which times are the most important to your child  in terms of nursing.  Those will be the last to go.  Pick whichever time he/she seems to need to nurse the least, and make that the first to go.  For instance, say his/her first session in the morning, before nap, and before bedtime are the top three.  But maybe your nursling isn't as adamant about nursing between breakfast and lunch - let that be the first session that you work on eliminating.  Then you want to put yourself in a position where it's not easy or convenient to nurse, and where your child  doesn't think about it - it's a lot harder to say no and make him upset than it is just to preempt him entirely.  So if you know that whenever you sit in a favorite chair (or at the computer or whatever) she wants to nurse, don't sit in that chair - seriously, if that means checking email or BZ while standing up the whole time, that may be what it takes!  :-)  If you know that he usually wants to nurse around 10am, offer him a favorite snack at 9:50, one that is enough of a treat that he won't immediately think of nursing.  If she often wants to nurse because she's getting bored, find ways to keep her entertained and occupied and getting your positive attention in non-nursing ways - plan extra trips to the playground, zoo, etc.    Sometimes distracting them with a special toy or game can do the trick, it's different for different kids. 
 
Once you've successfully eliminated one session and your nursling stops expecting to nurse at that time, then you can move on to the next.  For some children, the whole process can take a few months, for others it will go much more quickly (weeks or days).  It's much less painful and difficult for both of you if you do one at a time rather than a bunch at once though - work your way up from the easiest ones to the ones that seem like the most important to your little one.  If there are times your DH can help, get his help - for instance, when it's time to eliminate the bedtime nursing session, let DH start a new bedtime routine with your child, while you stay out of sight.  It may be hard the first few days, but believe me it is much easier than you trying to do bedtime without nursing if this is an important nursing time for your child.  Once your little one is used to the new routine and not needing to nurse at bedtime, you can always pick a night back up here or there as needed, but try to be as consistent as possible at first.  It really is much easier if he/she doesn't know you're right outside the door (or whatever), you might even want to leave the house and take a walk around the block (or quick trip to the store/starbucks/etc. - this can be a great time for catching up on chores or some valuable "you time" - maybe locking yoruself in the bathroom for a relaxing bath and glass of wine or special chocolate treat!). 
 
Limiting nursing and tips to stay sane
Some moms find that as their nurslings get older, it helps keep the nursing relationship manageable and positive for both mother and child if they institute some limits.  For instance, many moms are not as comfortable nursing a two year old in public as they were with a two-month old.  Sometime after the first year/18 months or so, they may start teaching their children that they don't always need instant gratification in nursing immediately if they are out in public (except in emergencies or extreme situations, like if the child has been injured or you are on vacation and can't go straight home to nurse!).  If baby asks to nurse in the middle of a grocery trip, mom might say "no nursing now, but after we pay for our groceries, we will go home and you can nurse then."  Some families may not believe in this, but for other families, it can be quite helpful and can also function as a good way to teach children to wait patiently rather than expecting instant gratification.  Again, what works well for one family and child may not work so well for another.
 
Some moms find that their children would be willing to nurse straight for hours if it were possible.  Especially if there are other children in the family, this may not always be an option!  Many moms have found that it helps their children to have a limit in how long a nursing session is - for instance, the child can nurse while mom reads one story, or sings a favorite song, or counts down from 20, etc.  After that, the child is expected to stop, but may have some snuggle time with mommy before mommy gets up.  This can help keep mom sane and can also help the child to understand that there are fun ways to be close to mom that don't involve nursing, which can help with the weaning process down the road.  Oftentimes, moms find that by partially weaning gently when they set limits such as these, it can help them to enjoy their nursing relationship more and wait longer before feeling the need to wean entirely if their child is not yet ready to do so on his/her own.  
ETA:  
 Here's a good article from Dr. Sears with some weaning tips for those who might need them:
http://www.askdrsears.com/html/2/T026400.asp
Here's another great Kellymom page on tandem nursing and nursing during pregnancy:
http://www.kellymom.com/bf/tandem/index.html
This book is highly recommended for tandem nursing/pg& nursing moms:
http://www.amazon.com/dp/0912500972?tag=kellysattachm-20&camp=14573&creative=327641&linkCode=as1&creativeASIN=0912500972&adid=04N6C9JT4HKP4A9G2HNM&