"Payed" vs paid

"Lead" as the past tense of "to lead", as in "yesterday, i lead them astray". This should of course be "led", though not as in Zeppelin.

Your and you're: Correct usage is "you're peeing on your shoes". "You're" is a contraction of "you are"; "your" is just a common or garden variety possessive pronoun, and as above, no possessive pronoun uses an apostrophe. The apostrophe represents something which has been removed, in this case the 'a' in "are", much like the missing 'i' from "is" in "it's".

Drifting off into spelling, "definately" for "definitely" always drives me into a paroxysm of loathing.

Another capital "supposedly" crime is "supposingly".

"They" is not singular. Trust me on this one.

"Weird" is weird in that an 'e' precedes an 'i' without a leading 'c'.

"People that..." is goofy unless you're deliberately trying to write like a pothead for comic effect; we prefer "people who". People are people, not things. (dannye's peeve, but also mine)

"-ant" used for "-ent", which I suppose is spelling more than grammar. Either way, take care with "sentence", "existence", "tendency", and a few others. "Dependent" vs "dependant": 'A' for adjective, 'e' for noun. (dannye's peeve, but also mine)