My DD is 3, and I confess to buying too many clothes for her.

I'm a "matchy matchy" type person, so every top needs a bottom to match, etc.
I do buy some of her stuff out of season when it's on clearance. Kohl's and Carter's store both have an unlimited time return policy. On the rare occasions where I've guessed the size wrong, I can take it back with no problem. I don't generally buy shoes ahead since the sizes are too hard to guess, except for at Kohl's, because I can return them easily even a year later.
I really like the Jumping Beans brand of clothes at Kohl's. They fit a bit smaller than Carter's brand, but they wash up nicely, and I can get them inexpensively. I personally think they're cuter than Carter's brand too, at least for toddler girls. The girls clothes seem to have about 8-10 assorted colors, so it's very easy to coordinate tops to bottoms. The trick to shopping at Kohl's is to have their store credit card, because they run 30% off sales about once a month. Even if you don't get the 30% off coupon in the mail (some flyers are 15% or 20%), you can still use the 30% code online, and they usually have a free shipping code too. (It's always easy to find the codes via Google.) As an example, Kohl's has a good sale starting on the 11th. Jumping Beans separates for infants (up to size 24 mths) will be $5.99 each. Take 30% off that, and it's $4.19 per piece. The upcoming sale is also offering Kohl's Cash, at a rate of $10 per each $50 spent. So, that's basically another 20% saved, for a final cost of $3.35 per piece. Another example is that they'll have Carter's 2 pc bodysuit/pant sets for babies for $9.99. Minus 30% makes those $6.99, and then after Kohl's Cash, you have a final cost of $5.59 for the 2 pc outfit.
I've also been surprised at the quality of the Garanimals brand at
Walmart. I bought DD a couple of cute summer outfits there this spring, and they've held up very nicely. I also like their Faded Glory brand 2 pc cotton pajamas, that come in a box. On the flip side, the clothes from Kmart are awful quality, including their Disney line. I caught a great clearance sale there last fall ($2.99 for 2 pc summer outfits) and bought 5 or 6 outfits for this summer. Every one of those outfits look awful now, even though they've only been washed a few times.
I also shop some at The Children's Place, but only at the outlet, which isn't that close to home. I like their adjustable waist jeans, and they frequently go on sale for $8.50 a pair for toddler sizes. Sometimes they'll have free shipping on the website with no minimum order.
I've went to a lot of children's consignment sales, and it's really hit or miss. I found a lot nicer stuff when DD was still in infant sizes. Every since she grew into toddler sizes, the clothes at the consignment sales are generally in not so great condition. I did go to one on Friday, and picked up a nice fall jacket, a Halloween costume, and 2 cute outfits. Everything else I saw was either seriously overpriced, or in poor condition. My best finds at consignment sales lately are usually dress shoes and toys.