I'm trying to capture the idea that Xp requires a fast, easy design, but perhaps not necessarily CRC cards.  For instance, on TeachingXp I discussed how I once taught Xp to a group where we didn't use CRC, but instead used a very stripped-down "UML Distilled, Distilled".  I've used both CRC and UML extensively, and I've seen that I can use either one without losing much design velocity.  Of course, I have to abandon much of UML's extraneous bits and pieces in order to make this work.  I generally only draw a minimal class diagram and a few  OID's when I'm doing a quick design.  If you limit yourself to this, it won't take a lot of time (BTW, I use big pieces of paper too, and don't even consider CASE tools)...

I think the key to what works for you may be if you are visually oriented or not.  If so, then UML's pretty pictures may work best for you. If not, then CRC may be a more natural modeling technique.  I've heard arguments for CRC where people say the visually oriented among us just orient the cards on a table, but personally, I like the way that the arrows can take on meaning (inheritance vs. association vs. composition) in UML.