Fred:
Yes, Mouser has good ease-of-use and it has a much larger variety of parts than the other suppliers.
First, though, you should check to see if Mouser itself has parts in stock that substitute well -- I was getting all frustrated by out-of-stock 1-watt resistors the other day when RJ posted a list of Mouser substitutes and the light bulb went off: spec out the part and then check Mouser first for substitutes (remember: capacitors can be of *higher* voltage and work fine, you just can't go lower -- but also be certain the dimensions work OK too).
Anyway, should Mouser come up a cropper, most people go with either Jameco or Digi-Key as a secondary place to order. I buy a lot of stuff from Jameco because it has a will-call window and is a 30-minute drive from my house (was there yesterday) and some items are cheaper there (resistors, except they don't carry 1-watters, darnit).
There's also Allied and Newark, but I haven't used them.
Hope this helps.
\dmc