All you have is $100 bucks or $1,000 bucks, maybe $10,000 grand. No problem, Sharebuilder.com can accomodate your measley investment of anything.
Or, try Tradeking (over in the right sidebar I have a clickable link), they have some spectacular deals going on right now (and they were rated the #1 discount broker by SmartMoney in 2007.)
This gives you no excuse to get started, instead of throwing that $20 spot on a bottle of rum that will leave you with a headache the next day, stick that loot into an account and get started! Be sure to read through my lessons though, so you don’t go in blindly and throw away all your money.
Keep in mind though, if you have generally more than $1,000 to invest, some of the other discounted brokers may have sweeter deals with regards to how many free trades and such you can make. It only makes sense to be diligent and look at multiple brokers to see who has the hot deal of the day.