The only advantage I know if trading the cubes QQQs is that you can do it in an ISA, and therefore your profits are tax free. ComDirect and iDealing allow you to trade these in an ISA.
If you are trading outside of an ISA and using a deep discount broker, such as IB, then you will need to buy in lots of 100 shares at a time, so 100 or 200 but not 134. Of course, if you want to buy oddlots (134 for example) then you can do it through more conventional brokers, but the commissions will be much higher.
As I'm sure you know, QQQ is a tracker stock which tracks the Nasdaq composite index. DIA (also referred to as Diamonds) tracks the Dow, so is a way of trading the Dow longer term through an ISA. The tracking stock for the S&P is SPY. If I recall, these are traded on Amex, so to follow them in real time you will need to fork out an additional $1 per month for the Amex permission.
If you want to trade shorter term, I would suggest you either use a spread betting company to trade the actual index futures, or trade the futures themselves. The latter, however, is definitely not for beginners, unless you like having brown trousers. :cheesy: