All providers give you FREE WEB SPACE, but you MUST include their ad banners in every page you build. Sometimes YOU can decide where to place the ads (Geocities), in other cases the PROVIDER will either instruct you about the position or place it automatically (Tripod). Another general rule: no sex, nudity or pornography allowed. No illegal content (passwords, crackz warez...). Always READ rules, terms and regulations.

The AMOUNT of FREE SPACE is NOT the ONLY important think you should think about. Always check the SPEED connection by browsing the company's site.
A slow connection will be frustrating for you and your homepage's visitors.

And remember: change the password they give you!

Good Luck!