This is mostly idle pondering for me. I have a character created under gestalt rules for a campaign I might run, who's a rogue/something (likely a dash of swordsage) gestalted with a Beguiler, which is fluffed as the innate magical power of his race brought out via a magical graft given to him by his father. However, the character's origins are from a campaign my friend is running, which ended with him dying and his father sending a servant to retrieve his body to be resurrected. Since then the party's wandered off into Ravenloft, which is where my current character is, but eventually we (well, they) will be returning to their prime plane, and since my character is a Bone Knight from a different plane he wouldn't return with them. So, I had the fun thought of my resurrected character returning to help out once they returned!
The problem is trying to figure out how to mesh Beguiler and Rogue together without gestalt rules. My initial thought was going something like Rogue 1/Beguiler 4/Unseen Seer 10/Arcane Trickster... Basically the 'standard' arcane rogue with wizard levels swapped out for beguiler levels. However, I took another look at the Beguiler Class and love its sixth level ability... Which changes things a bit.
Basically, I want to create an arcane rogue which fights like a rogue (being sneaky, feinting, and using sneak attack thanks to Unseen Seer/Arcane Trickster and Hunter's Eye), supported with illusion and enchantment spells for buffs and control. Which is why I thought about going six levels into Beguiler, since he'd now be able to swift action feint (and when potentially combined with surprising riposte, could lead to a lot of fun), then again, there is also Greater Invisibility which does just as well without three feats to cost. It doesn't need to be Beguiler, but the class meshes extremely well with the concept and I'd much prefer a spontaneous spell caster who doesn't have to lug around a spell book.
I'd figure I'd pump Int over Dex and grab the Fey Mystery Initiate feat (the character already had it, to boot!), which will make him surprisingly hardy for a rogue type with a d6/d4 hit die.