I used to use AIOSEO then discovered SEO Ultimate, from the WP directory.
Builds automatic internal links to a post, which is one of the major reasons I use it - but tons more:
1) Competitive analysis for KW's (using simple search strings in Google, but saves times in support post composition).
2) Adds the microformats data to Google (this is for reviews: displays 1-5 stars in Google SERPs after a while...it took my site a few months but they're there now).
3) Allows full access to .htaccess and robots.txt from within your dashboard.
4) Manages all the AIOSEO metadata but better IMHO, because you can do it globally.
5) Adds the canonical URL for you if you want (so no more dupe content worries).
6) Adds the ability to add a code to any page - like if you want a banner ad, for example, to all pages/posts...or webmaster tools verification metadata, etc.
7) Adds a link masking ability which is a superior form of nofollowing a link (by creating a directory of your link, then adding the nofollow robots meta tag to that directory: superior to the rel=nofollow tag which essentially just divides your PageRank on internal links...for those of you doing PageRank sculpting)...basically think of it as a great free cloaker for your links.

Adds a widget so you can display links to related categories...good for siloing a website for SEO architecture.
Ugh. Sorry. Going all crazy here.
Just meant to say, "I love SEO Ultimate."
Anyone who bought my Duct Tape SEO book knows the in's and out's of how I use it to rank lots easier these days, among other fun SEO shtuff.
