Question
Thank you for your quick reply.  I've done a little web research on both conditions and I'm pretty sure that's not what this is.
This is a solid mass on the underside of my big toe - it is on the flat, smooth part ...on the bottom, where you walk.  It has not affected the skin at all, and doesn't appear to be liquid or gel which could be drained.  It also seems to come and go for no reason.  The toe tends to feel a little numb when the lump is present. Maybe a podiatrist is the best bet, huh?  I'm new to this area and don't have a primary care doc yet, let alone a referral for a specialist :(
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Followup To

Question -
I just started a running program (Couch Potato to 5k in 8 weeks).  I'm on the 6th week and during my last run, I noticed an odd sensation in my 'big toe' on my left foot.  It felt like I was stepping on something every time I put my foot down.  In examining the toe, I noticed a small knot under the skin, it is sticking out enough to cause the skin to be white.  It isn't painful, just a little annoying.
When I push it, there is a little resistance, making me think it is more solid than fluid.  It is roughly the size of a pea.  Any thoughts/suggestions?
Thank you!

Answer -
Amy,

This sounds like a soft tissue mass and the most common are either plantar fibromas or ganglion cysts, both benign conditions.  Typically these are nothing to worry about and they are caused from pressure and stress to the foot.

However, I would see a Podiatrist as there may be something else going on that should be treated.

Good Luck and let me know how it goes.  

Answer
Amy,

After your response, this sounds a little different.  If you get numbness then it could be an enlarged nerve from irritation.  
It is also still possible that this is a ganglion cyst or mucoid cyst.  
These can become firm when they fill with fluid and at that point they may feel solid. They then may disappear as the fluid leaves the cyst. The fluid will typically come from the tendon or joint.
If they are small, you may not be able to drain fluid.
I would see a Podiatrist.

Where do you live? Maybe I know a Podiatrist in your area.  You never know!

Good Luck.