Is there any way to keep pepper plants relatively small?

[stevie]

if you let it stay in a small container and let it get too much roots and later in the future decide to grow it larger it will take much longer to recover than if you just pruned it to keep it small and was in a proper size pot.

 

[nephila]

As someone said, small pots. I keept alot of my peppers in solo cups this year due to bad weather and no space due to renovation of the house. They where in there for over 6 months and doing great.....they where just small

 

[ribbedturtleneck]

I have some extras, seeds started in January that never got potted up, still in solo cups. A 7 pot, a bhut, a butch t, and an India Jwala. Each is relatively healthy, about 6-7 inches tall, and at least one pod on it. May get put in half-gallon pots to overwinter, or maybe not. Peppers make great little house plants if you give them sun, water, and nutes.

 

[DMF]

The OP apparently is planting in ground, so all the answers - some of them good ones - that include root restriction are inapplicable.
 
backyardpepper,

1. Don't plant varieties that like to grow 7' tall.  Some do, most don't.
2. Provide less-than-optimal growing conditions: poor soil, little sunlight, no ferts
3. Prune.

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Now, let's do something that we should have at the start of this thread:  Ask, "Why?"
 
Why are you growing?  Fruit yield?  Ornament?  Curiousity?  These are all valid motives, of course.  But where you place your priorities implies a method.  Or implies letting them grow as they will.

How small will they be? I'm guessing that will depend on how much I top them?

Oh and how far apart should I put the plants when I put them into the ground?

 
C'mon!  Tell us what you are planting!  Peppers are a rather diverse crowd and there are few generic answers. Also, what are the conditions?  Do you expect much wind?  How much sun will they be getting?  And back to your priorities - are you concerned primarily with yield?  or is ornament important too? 
 
For instance, a nice thick pepper hedge won't yield quite as well isolated plants, but looks nice and is more wind resistant.