Umbrae's Tower http://umbraes-tower.blogspot.com/2012/07/sharepoint-2010-and-list-picker-custom.html

ListPicker.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.WebControls;
using System.Web.UI;
using Microsoft.SharePoint;

namespace QuickLinks
{
    public class ListPicker : EditorPart
    {
        private TextBox txtListUrl;
        private Button _selectList;
        private String WebPartName = String.Empty;

        public ListPicker(string webPartID, string webpartname)
        {
            this.ID = "ListPicker" + webPartID;
            this.Title = "Select a Quick Links Enabled List";
            this.WebPartName = webpartname;
        }
 
        protected override void CreateChildControls()
        {
            base.CreateChildControls();
            txtListUrl = new TextBox();
            //_listUrl.Enabled = false;
            Controls.Add(txtListUrl);
            _selectList = new Button();
            _selectList.OnClientClick = "javascript:launchPicker();";
            _selectList.Text = "...";
            Controls.Add(_selectList);
            Controls.Add(new LiteralControl("<br /><br />"));
        }
 
        public override void SyncChanges()
        {
            EnsureChildControls();
 
            if (WebPartName.Equals("QuickLinks"))
            {
                QuickLinks.QuickLinks webPart = WebPartToEdit as QuickLinks.QuickLinks;
                if (webPart != null)
                {
                    txtListUrl.Text = webPart.qlListProp;
                }
            }
         }
        public override bool ApplyChanges()
        {
            EnsureChildControls();


            if (WebPartName.Equals("QuickLinks"))
            {
                QuickLinks.QuickLinks webPart = WebPartToEdit as QuickLinks.QuickLinks;
                if (webPart != null)
                {
                    webPart.qlListProp = txtListUrl.Text;
                }
            }
            return true;
        }
 
        protected override void OnLoad(EventArgs e)
        {
            base.OnLoad(e);
            string webLocale = SPContext.Current.Web.Locale.LCID.ToString();
            Page.ClientScript.RegisterClientScriptInclude("PickerTreeDialog", string.Format("/_layouts/{0}/PickerTreeDialog.js", webLocale));
 
            RegisterSelectListScript();
        }
 
        private void RegisterSelectListScript()
        {
            StringBuilder launchPicker = new StringBuilder();
            launchPicker.Append("<SCRIPT LANGUAGE='JavaScript' >");
            launchPicker.Append("var lastSelectedListSmtPickerId = '';");
            launchPicker.Append("function launchPicker() {");
            launchPicker.Append("   if (!document.getElementById) return;");
            launchPicker.Append("   var listTextBox = document.getElementById('" + txtListUrl.ClientID + "');");
            launchPicker.Append("   if (listTextBox == null) return;");
            launchPicker.Append("   var serverUrl = '\u002f';");
            launchPicker.Append("   var callback = function(results) {");
            launchPicker.Append("       if (results == null || results[1] == null || results[3] == null) return;");
            launchPicker.Append("       lastSelectedListSmtPickerId = results[0];");
            launchPicker.Append("       var listUrl = '/';");
            launchPicker.Append("       if (results[3].charAt(0) == '/') results[3] = results[3].substring(1);");
            launchPicker.Append("       listUrl = listUrl + results[3];");
            launchPicker.Append("       listTextBox.value = listUrl;");
            launchPicker.Append("       disablePostbackControls();");
            launchPicker.Append("       " + Page.ClientScript.GetPostBackEventReference(txtListUrl, string.Empty) + ";\n");
                        // __doPostBack('ctl00_MSOTlPn_EditorZone_Edit0g_15f9eea6_e2c8_4a1f_9772_0a32b6394eb2_CBQToolPartshowItemsFromListRadioButton', listTextBox.value);
            launchPicker.Append("   };");
            launchPicker.Append("LaunchPickerTreeDialog('CbqPickerSelectListTitle','CbqPickerSelectListText','websLists','', serverUrl, lastSelectedListSmtPickerId,'','','/_layouts/images/smt_icon.gif','', callback, '', '');");
            launchPicker.Append("}");
            launchPicker.Append("</SCRIPT>");

            if (!Page.ClientScript.IsClientScriptBlockRegistered("launchPicker"))
                Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "launchPicker", launchPicker.ToString());
        }
    }
}

QuickLinks.ascx.cs

namespace QuickLinks.QuickLinks
{
    public partial class QuickLinksUserControl : UserControl
    {
        // For Custom Properties
        public QuickLinks WebPart { get; set; }

        protected override void OnPreRender(EventArgs e)
        {
            base.OnPreRender(e);
            // For Custom Properties
            this.WebPart = this.Parent as QuickLinks;

            // Rest of your code

        }
    }
}

QuickLinks.cs

using System;
using System.ComponentModel;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;
using System.Collections.Generic;

namespace QuickLinks.QuickLinks
{
    [ToolboxItemAttribute(false)]
    public class QuickLinks : WebPart, IWebEditable
    {

        private string _qlListProp;

        [Browsable(false)]
        [Personalizable(PersonalizationScope.Shared)]
        public string qlListProp
        {
            get { return this._qlListProp; }
            set { this._qlListProp = value; }
        }

        // Visual Studio might automatically update this path when you change the Visual Web Part project item.
        private const string _ascxPath = @"~/_CONTROLTEMPLATES/QuickLinks/QuickLinks/QuickLinks.ascx";

        protected override void CreateChildControls()
        {
            Control control = Page.LoadControl(_ascxPath);
            Controls.Add(control);
        }

        #region IWebEditable Members

        EditorPartCollection IWebEditable.CreateEditorParts()
        {
            List<EditorPart> editors = new List<EditorPart>();

            // Add the base editor parts
            
            editors.Add(new ListPicker(this.ID, "QuickLinks"));
            return new EditorPartCollection(editors);
        }

        object IWebEditable.WebBrowsableObject
        {
            get { return this; }
        }

        #endregion
    }
}