We actually have quite a few things from Homebase/Argos (depending on which is cheaper), the Strand collection being a particular favourite (sideboard, display cabinet, coffee table, tv stand... they seem to have increased their prices by at least 25% since we bought however). Most of that range look more expensive than they are i.e. we get positive comments about them and are pre-built rather than the usual flatpack you would associate with the chain.
Few items from World of Pine (dvd/cd racks, bookcase, mirrors...)
Recently started shopping at Ikea too, good for cheap items.
Got a few random hand-me-downs as well.
Worst thing I think is that we don't have a totally consistent theme i.e. the majority of our items are oak or oak finish but e.g. we have a much lighter shade kitchen table, nest of tables, shelving tower etc. Nursery has white furniture throughout (cot, 2x chest of drawers, storage unit, tub chair etc) except for a cheap Maple wardrobe we got a couple of years prior and now looks out of place

I used to reckon theming was overrated and I would just buy whatever I wanted for practical reasons as long as it looked smart, but now I think you can do a lot worse than just buy a full set from the same range even if you aren't totally convinced by all the pieces. In an ideal world I would replace the wardrobe in my son's room with a white one.