Awesome advice! Thanks, I will have to look up the Chameleon PrC now.
Races of Destiny, page 111. It's a fantastic class for versatility, and a natural progression for what the Factotum does, however you need to decide if you want to give up the Factotum's higher level abilities to take more levels in Chameleon for it's super-fantastic abilities.
IMHO, the important levels to take Factotum to, when considering multiclassing, are Level 8 for the ability to take an extra Standard action in a turn, Level 13 to ignore damage that would kill you from one source, and level 18 for access to level 7 arcane spells.
Chameleon grants you adjustable stat bonuses, various class features from other classes, and access to ALL spells up to level 6. It is worded to include Any Arcane and Divine spell lists, so Assassin spells, Hexblade spells, Druid spells, as well as the sor/wiz and cleric spell lists become available to you. Which will aid our ability to manufacture magical items.
However, Factotum up to level 18 gets access to arcane level 7 spells. My understanding is that Artificer can emulate a spell list up to level 9 spells, so the access to another level of spells might not mean as much to you.
You have multiple good options. Enjoy!
Edit: Oh, a useful application of the rotating feat is to emulate the coveted "Craft Construct" feat, since Artificer doesn't naturally get that. Build your own army for extra Pwnage.
Another creative application is the "Craft Portal" feat, if you have 100 days and 100,000gp to spend, you can create permanent doorways across reality. Much fun.
other useful PrC dips for the Factotum are:
-Mindbender, 1 level dip, to gain Telepathy and than take the Mindsight feat, to "see" every creature with an Int of at least 1, know it's intelligence score and it's creature type. And telepathically talk to people.
-Exemplar, one or more levels, to gain amazing increases to your skill checks. For a single level dip, you gain a +4 to one skill you have at least 13 ranks in (UMD!), and select a number of skills equal to 1+your Int Mod (which should be high) to be able to take 10's in skill checks regardless of conditions.
Factotum Handbook
Another Factotum Handbook