I agree with all the above suggestions...Here is another...how about planning a few free family nights with refreshments and perhaps have a cultural arts assembly included. Every year the PTO pays for these assemblies and the parents never get to see them. When I was PTO pres I made sure we had a social evening with a program included....it was really well received & appreciated.
Personally I hate the idea of just giving (donating) funds to the school Principal and allowing him to decide how to divy it out. To me those funds, extra or not, are very important to all that we want to do. And having a little extra is always nice.
IMO, your expected income for the year should about coincide with your expected out, per your planned budget. So if last year you spent $1000 on new books for the Library, then you should have that allocated for next year and plan to spend the same. If you do this for everything then you should have a pretty balanced budget. Although I would recommend trying to have slightly more come in that what goes out, just inc case. So say you normally bring in $20K for the year, try to have your budget set to use around 18-19K, so you'll have that small buffer...
But in a situation where you have extra, due to a build up over the years, then I would say look for a special project to spend it on. Talk with the Principal and see what his priorities might be. For example, out Principal is very much in to technology and this year we purchased SMART boards for some of the classes. If we had extra money I would imagine that he would want more of those, ultimately having one for every class. Another place to possibly focus is the playground.
I agree with dlf: you need to have a goal for your money. While it's great that you don't turn down new requests, I think that could also get you in the position of paying for a mediocre idea early in the year and then finding you don't have enough money at the end for a great idea.
Perhaps you need to revise your budget to account for the grants. Leave a chunk for mid-year funding requests, but have a plan for the rest.
Spend it! No matter how much we make there is always a long wish list. Teacher's workroom - does it need new equipment. Technology - we could spend thousands just beginning to keep up with technology needs. Media Center - our librarian has a wish list a mile long, all purchases benefit the entire school. Music Program - new instruments, CDs, DVDs, props. PE dept - new equipment for new games, how about a climbing wall? When we ask teachers to meet in teams and come up with their top needs, we generally get at least $10,000 in items.
The parents are supporting your fundraisers because they trust you with their money and they want their kids to have a better education. If you don't spend the money (and tell them about all the fabulous things you bought) they'll stop supporting your fundraisers. Why should they give, if you already have money? Do some research and set some goals. You should be able to come up with a list of what you will buy this year and your goals for the next two years.
We are called the forces at our schools but it's the same at pto. We use the money we make for the kids activies like sometimes we pay for a field trip, we have helped pay for mulch for the playgrounds. Your making money for the kids right - so if you have funds you should see what they could be used for.
If you have money then you should put it back into the school some how. there are lots of things you could be doing with the money to make parents feel like their kids are going to benifit from the hard work they put into it.