Patterns at the chain fabric store

Your local JoAnn or Hancock will carry these patterns. Often they go on sale for $1 or $2, sometimes 5 for $5 or 10 for $10. Opinions are mine.

Simplicity
2354 Women's "colonial dress. quite a bit wrong, pass.
3635 Women's 18th century undergarments to be worn under 3637 Shift, stays, panniers. Rather good for the usual offerings
3637 Women's 18th century gown to be worn over 3635 Rather good for the usual offerings
3644 Children's Pirates of the Caribbean Pirate (licensed by Disney) costume. The coat and waistcoat are actually not that bad, the breeches are not good, the shirt is not a period cut. 
3677 Women's pirate costume. complete fiction, no pirates allowed at the party.
3723 Women's "colonial" costume, quite a bit wrong, pass.
3725 Girls version of 3723, pass
4055 Women's Regency gown patterned by Jennie Chancey of Sense & Sensibility Unfortunately the corresponding undergarment pattern 4052 has been discontinued. Very good for the usual offerings.
4092 Women's 18th century gown styles after PotC Not as good as 3637 (calls for a zipper!) so pass it up.
4923 Men's 18th century costumes styled after PotC Not as good as 3644, the pants are still very wrong.

McCalls
6139 Women's and Girls "colonial" dresses Don't bother

Butterick
3072 Men's "Revolutionary War" costume. Forget the hat. the pants are still wrong, shirt is not a period correct cut. could be reworked to something better.
4254 Corsets for the 18th and 19th century. You want View A or B. there are some issues with these, but overall it isn't a bad pattern. View B was also included in pattern 4484, which also had other undergarments, now Out of Print

6630 Women's "regency" gowns Not terrible, Simplicity 4055 is better though

You may also like to read some other reviews

Jessamyn covers the regency patterns (including ones from other companies I have not included)
Greater Bay Area Costumer's Guild has an excellent pattern review section.