What is my [DSM] maintenance schedule?

There are a lot of threads on mods and upgrades, but it is very important to make sure that all the maintenance is done on your car. Check your repair manual for the complete list, here is the minimum list that I recommend:

Every week or every 250 miles or when you get gas/fuel:
1) Check engine oil level
2) Check brake fuild level
3) Check tires and tire pressures

Every 3000 miles or 3 months
1) Change engine oil and oil filter
- The most commonly used oil is synthetic 10W30, 10W40 and 15W50.

Every 6000 miles or 6 months
1) Rotate tires

Every 15000 miles or 12 months
1) Change PCV valve. (When you buy it, blow on one end and then blow on another, you should only be able to blow one side. If you can blow on both sides, it is bad, get another one)
2) Change spark plugs
- If you have no or mild mods get - NGK BPR6ES or Autolite 63 Copper
- If you have moderate mods get - NGK BPR7ES or Autolite 62 Copper 
- If you have a LOT of mods get - NGK BPR8ES
Gap plugs to 0.028 to 0.031". Use no other plugs. No platinum or dual electrode stuff. 
If you are experiencing stuttering from high boost, try to gap plugs in the range of 0.020" to 0.024"

Every 30000 miles or 24 months
1) Replace air filter
2) Spark plug wires - (I use NGK premium wires: part# ME77, stock# 8100)
3) Coolant flush - 50/50 (with one or 2 bottles of water wetter if you want to use it)
4) Change the tranny fluid - most commonly used on manual transmissions is Pennzoil Synchromesh, which is a cheaper alternative to BG Synchroshift. After having issues with Synchomesh for a while (it is too thin), I switched to a combo of Redline heavy and light. 
5) Change the transfer case and rear diff fluid (if you have AWD) - most commonly used gear oil is Redline Heavy Shockproof gear oil.

Every 60000 or 48 months
1) Replace fuel filter
2) Timing belt change: A complete list of 60k timing belt service would include all these:
- Timing belt
- Balance shaft belt
- Timing Tensioner
- Water pump
- Timing belt tensioner pulley
- Balance shaft tensioner pulley
- Idler pulley
- Crank seal
- Oil pump seal
- Balance shaft seal
- 2 Cam seals
- Harmonic balancer
- All other belts
Get only MITSUBISHI parts for the list above. OEM part does not always mean that the part is made by MITSUBISHI. If you don't know where to but parts from, this is a good start - Where Can I Buy OEM Parts Besides Junkyards and Ebay? - DSM Forums.

If your car is old, go ahead and replace all the vacuum hoses. RRE makes a good kit here - RRE's Larson Silicone Hose Kit