Hi Jude. You don't say where you are from so what you could do largely depends on whether you mean front yard in the USA sense or the UK sense. If you mean 'yard' UK-style, i.e. a paved area then to make it more interesting with plants rather limits you to containers but if you mean 'yard' US, i.e. a front garden, then you can just pop plants directly into the ground below the gravel (if you have membrane down just cut holes in it) or, of course you can also use containers. Terra-cotta looks great against gravel but if you use this type for pots then I wouldn't try to economise by buying the plastic ones. A few genuine ones would be nicer than a lot of plastic.

Your type of plants is of course a matter of taste and zone. Cordylines, palms and flaxes are traditional with or without pelargoniums to give a European look. But if you like thistle type plants a 'dry' garden of teasels, echinops, eryngium etc. looks great. But if you love lupins and peonies then just plant lupins and peonies. You can only please yourself.

A picnic/barbecue area may be nice, if it appeals, with table, chairs, b-b-q etc. Or if there are young children in the family then a play area with swing, slide, roundabout etc. can look great and is useful.

You really should develop it as an outside room to do what you want when the weather is fine, but whatever you decide on then do incorporate plants. But of course, this is a garden forum so I would say that.

There are some very beautiful urns around.
Very tall and elegant and would look fabulous as a feature there.

But remember that particularly in front gardens / yards, containers are very vulnerable to theft.

I wouldn't spend a fortune on a fabulous urn just to have some toe-rag pinch it. Go for dramatic planting in less expensive containers.

With white gravel as a background bright colours would shine out and really contrast. Imagine a black painted tub, pot or wooden container with some scarlet geraniums in it. Or any other colourful plants that take your fancy.

The kind i'm thinking of would be very heavy indeed and not at all easy to maneouvre - not easy for that type of person to pinch.

I agree with all of the above and would advise having a focal point, whether it be a magnificent pot or a dramatic plant. Without something to catch the eye, a scatter of pots can lose impact, but placed in a planned way around a focal point can look splendid.

The white looks very good and one way of making it look better and breaking the colour up would be to put some other decorative aggregate around the edges
have a look at some of the pictures in the gallery at
www.decorativeaggregates.com it may give you some ideas and you can buy what you need online from them.