Normally, I look through the manual to see what is included with the services. Generally, they are pretty lame and very expensive.
If it is a newer car, it probably has platinum spark plugs which most manufacturers don't recommend changing for 100k miles. You do, however, need to get your oil changed regularly at 3500. Some manufacturers recommend up to 5000 miles, but I'd be a bit afraid of going that long with nonsynthetic oil.
If your car has grease fittings, these will need to be lubed regularly. Get yourself a grease gun and do it with every oil change if you decide to do them yourself. If you take it somewhere for the oil change, they should do it for you.
Also, you should get your coolant system flushed (check manual). I usually do this about every 50k if the car uses the green coolant. Transmission and axle fluid are the other maintenance items that are covered by the services. These should be changed as per the servicemanual recommendations. What I normally do is pick a service that performs a lot of stuff that I don't/can't do. For my last car, it was the 75k service which changed all my fluids for $200-300.
Other than that, check your belts every so often for cracking.