Each seo software has its own strength. However, I could say software can help you as partial for many tedious seo jobs but cannot help your website archive high ranking or keep its ranking stable. You may consider reading this thread for more info. P.S. IBP is the best seo software to help you analyze on-page factors throughly. It is good and worth to spend on anyway.
IBP and WebCeo are good one try there free versions and if you found them useful go for paid versions.
I'm doing a review of popular SEO tool SEnuke at this thread http://forums.digitalpoint.com/showthread.php?t=1794735
This site offer nice reviews oof couple of SEO software. The good thing is that they are on affiliates for them .... just check it out http://www.seosoftware.net
Best seo software is theseotoolkit.com A comparison table with all popular seo software: http://multimedia.md/seo-software.html
Senuke is over $140/month. way too expensive. Anybody know anything about Traffic Magnet? seems it's new competitor... would love to get opinion ...