You will need more Controllers
As the Wii comes with only one Wiimote and one Nunchuk you will probably want to buy extras so you can play games with your friends and family. Extra Wii controllers and nunchuks helps take the gaming experience to another level. Trust me Wii Sports is much more fun playing against a Human!
Wii Sports Pack
The Wii sports pack features a range of cool controller extras that make the games more realistic, these attachments include. A Golf Club Grip, Baseball Bat and mini Tennis Racket Grip, all of the add-ons quickly attach quickly and to the Wii-mote.
Wii Steering Wheel
The Wii steering wheel is a simple but effective add on to the Wii-mote, I find that holding the Wii controller with out one and playing car games just fees wrong. The Steering wheel makes it feel more natural and extends the game play reality.
Better AV Cables
When you buy the Wii it comes supplied with some basic RCA cables that are lets face it a bit old school! If you are lucky enough to own a Plasma TV, DLP or LCD Screen then a simple way to gain extra quality is replace the cables with either Wii component AV cables or a Wii S-Video cable. The Wii is not HD like the PS3 or Xbox360 its still a fast way to get a better picture with minimal costs.
Controller Docking Stations
If you're a hardened gamer like myself you will notice that the Wii Controllers have a real appetite for AA batteries. There are many docking stations for Wii controllers that replace the standard alkaline batteries for rechargeable ones. The Wiimotes simply charge up whilst not in use making sure that when you come to play you're not left feeling flat.
If you plan on making use of the Wii's backwards compatibility then the Gamecube controller is a must, they can be picked up on eBay for next to nothing. You can even buy the cordless Wavebird controller for wire free gaming.
SD Memory Card
The Wii is only supplied with a small 512mb SD card, it's not a huge issue if you only play a couple of games but you can soon fill the card up with multiple game saves. I personally purchased a couple of 2gb cards just in case I run out of space, it's a low cost add on and definitely worthwhile.
Infra-red Sensor Bar
The Wii comes with a infrared sensor bar but it makes sense to purchase a spare, they're not built with strength in mind and can become easily damaged, i have a pet rabbit who chewed through the cable! I had to wait a week for a replacement! Save yourself from boredom and buy a spare sensor bar.
Wii Points Game Card
The Wii points system is one of the best features of the Wii, it allows you to purchase classic games from the old Nintendo Platforms. My personal favorites are Super Mario World and Mario Kart (SNES). You can buy Wii Points online or buy prepaid Wii points cards. The current rate is 100 Wii Points per US Dollar.
Guitar Hero or Rock Band
Whilst not necessarily an accessory, Guitar Hero and Rock Band are probably the best Wii games out there at the moment. Either one of these games are an absolute necessity! Please go and buy this game, you will not be disappointed.