The purists in the audience will tell you to go get a hydrometer - it's really the only way of knowing for sure whether your fermentation is complete. They're maybe $6 at your LHBS. You can use the plastic case it comes in as a sample column and pull samples with a $2 turkey baster from the store (don't use your greasy kitchen turkey baster - buy another one and use it just for samples).
Having said that - if the krausen has fallen, and the yeast has dropped out, and the beer looks quiet and clear, and the ferment seemed to go well, then it *probably* is OK to bottle. Maybe. I've winged it with small batches just because taking samples out of a 1-gallon fermenter bites into your yield, but I *was* winging it.
I've warmed up to using a hydrometer as that is also a perfect excuse to sample your brew. I always drink my samples - to avoid contamination of course! Also knowing the SG has truly stabilized and is at the anticipated final gravity will give you peace of mind as to when to bottle. It's also great for getting a feel on how long your ferments actually take.